Two days later, Zan Wanshou and Le Quanan finally opened the waterway and arrived at the south gate of Chengdu, and the naval gunners who were holding their breath could finally show their skills. Solid shells flew towards the city walls, smashing the Mongol trebuchets and ballistae, and the soldiers were either killed or wounded, and even many of the Mongol soldiers hiding behind the battlements also died under the blown rubble. Although the iron artillery cast by Liu Heima with a lot of money carried out a counterattack, it did not cause damage to the Thunderbolt gunboat because the range was too short. Le Quanan saw the Mongolian army counterattacking with artillery, and immediately became angry. In his opinion, the Mongolian army should have obediently accepted the baptism and education of the Thunderbolt artillery, and dared to fight back, is this worth it? Immediately, he ordered the gunboats to fire at the artillery on the city walls. Although the Mongolian artillery was protected by civil and wooden bunkers, it could withstand the concentrated fire of dozens of heavy guns, and after a few rounds, not only the artillery was destroyed, but even the city wall where the artillery was placed was also bombarded.

At the same time as the naval forces shelled the south gate, two infantry brigades of the field division also shelled the west and north gates. As in the case of the South Gate, the siege weapons and defenses on the walls were quickly cleared; The difference is that the navy can only shell the city wall near the water and cannot shell the south gate tower on the side, while the two infantry brigades can not only shell the front city wall, but also bombard the west gate and the north gate tower. These two city gates were shattered but did not collapse, it turned out that the Mongolian army had already blocked the city gate hole with huge trees and stones, so it seems that Liu Heima was determined to defend it. Knowing that he could not confront the Thunderbolts head-on, he planned to engage in street battles with the Thunderbolts in the city. It is said that even if the Thunderbolts have melee weapons such as grenades, they have to fight house by house, and even if they win, they will be a miserable victory.

After several rounds of heavy shelling, the Thunderbolts' artillery gradually became less powerful. On the one hand, the hot barrel needs to be cooled down, and on the other hand, the ammunition consumption is too much. Although Ouyang Xuan said that he should not be stingy with ammunition, and there was also a large amount of ammunition stored in the rear, but the ammunition always needed to be transported from the rear for a long time. Seeing that his countermeasures were effective, Liu Heima's mind became active again. After nightfall, he sent men to the four gates—the east gate was the messenger sent to Genting City, and the west, north, and south gates were sent three teams of dead soldiers. The dead men were carrying canisters of fire oil and were ready to burn the Thunderbolts' gunboats and artillery.

For the night attack, Cao Ergou had already made full preparations. In order to prevent the Mongol army from touching the snails at night, Cao Ergou ordered people to lay mines in front of the artillery positions and sentry posts, dug many pits, and scattered many triangular nails. After the dead soldiers of the Mongolian army who attacked at night stepped on the mines, they attracted the fire of muskets, and the fire oil they carried was ignited, and they suddenly turned into giant candles in the shape of people running wildly. Compared with the night attacks at the West Gate and the North Gate, the dead soldiers of the Mongol army at the South Gate had some results - burning one gunboat and two escort ships of the Thunderbolt Army. In fact, Le Quanan and Zan Wanshou also made preparations to deal with the night attack, but they underestimated the effect of the fire oil. Although the dead soldiers of the Mongolian army who attacked at night were killed in the water, the oil floated on the surface of the water and drifted with the water, igniting the three warships at the front. The best way to extinguish the oil was to cover it with sand and dirt, but for a while these things could be found there.

For the next three days, the Perak army did not carry out large-scale artillery bombardment, but continued to fire sporadic artillery into the city day and night, with the aim of making the Mongol army unable to live in peace during the day and sleep poorly at night, so as to deplete their morale and fighting spirit. After the failure of the night attack on the first day, Liu Heima sent people to carry out a night attack on the second day, and was also wiped out again. After knowing that the Thunderbolt Army had been prepared, he also died to sneak attack this heart. He decided to hold on to the end and wait for reinforcements to arrive, hoping to turn the tables like the last battle of Chengdu. More than two years ago, when Pu Ze's Sichuan troops attacked Chengdu, Liu Heima and a group of Mongolian generals defended the city, and the Song army had captured half of Chengdu at that time, and the situation was even more critical than today. With the cavalry of the New Ring and Lizhou Wang Dechen coming to help, Pu Zezhi was defeated by the two sides, and was chased all the way to Chongqing by the Mongolian army.

Liu Heima made a wishful thinking, how could Ouyang Xuan not know? This is also the reason why he ordered Huang Dagen to hold on to Genting City after taking it. As long as Genting City is in the hands of the Perak Army, the Mongolian reinforcements from the direction of Dongchuan will not dare to advance boldly, otherwise the grain road will be under the threat of the Perak Army. Of course, the Thunderbolt army is not in a hurry to attack the city, which does not mean that it will fight a war of attrition with Liu Heima. On the one hand, the war situation dragged on for a long time and was very easy to change, not to mention that the Mongolian army was unwilling to lose western Sichuan, even Yu Xing and many other high-ranking officials of the Southern Song Dynasty were unwilling to see the rapid expansion of the strength of the Perak army. On the other hand, although the Thunderbolt army has strong economic strength, it cannot withstand long-term attrition. Ouyang Xuan's plan was to drive the Mongol army out of western Sichuan by September in order to obtain the grain that was about to be harvested and to plant summer grain. At present, there are more than 30,000 laborers involved in logistics and baggage transportation, and if the war drags on until after September, it will inevitably affect industrial and agricultural production. More importantly, as soon as the summer rainy season passes, the amount of water in the river becomes smaller, which will seriously affect the combat effectiveness of the naval army.

"The lesser of two evils", so between the war of attrition and the brutal street fighting, the Thunderbolt army top brass unanimously decided to choose the latter. It's just that before the siege, Ouyang Xuan prepared to shell for a few more days to wear down the morale of the Mongolian army, and adopted the method of "encircling three and one", in addition to the reason for the lack of strength of the Thunderbolt army, it was also to prevent the Mongolian army from being trapped and fighting under the siege on all sides. For the upcoming street fighting, Cao Ergou and Zan Wanshou both coincidentally adopted a ten-person squad as the basic combat unit. Of the ten, there were three swordmen and shieldmen, three spearmen and three light artillerymen, and one demoman. Light artillery bombardment is used against distant enemies, grenades are thrown at medium range, and hand-to-hand combat is fought by sword and shield men and spearmen at close range. As for the enemy's strong fortifications, blasting was carried out by gunpowder packs.

At dusk on the fourth day of the siege, more than 1,000 cavalry from Kudu appeared outside the east gate of Chengdu. At this time, Ouyang Xuan had already obtained the news of Huang Dagen's entry into Genting City through the Flying Pigeon Transmission, and also got the news that Hudu and Jiagu Dragon Ancient had retreated respectively. In ancient times, Jiagulong led an infantry army, and his whereabouts were easy to track, knowing that they retreated to Jianzhou, but the whereabouts of the cavalry in Hudu were erratic, and they only knew that they were about to go in the direction of Chengdu. The enemy hidden in the shadows was the most terrifying, when they saw the appearance of these cavalry, Ouyang Xuan and Cao Ergou were relieved, and they ruled out an uncertain factor, and immediately ordered to prepare for the cavalry charge.

When Liu Heima saw that Kudu had brought cavalry here, he was also very relieved. In fact, he didn't want to flank the Thunderbolt army with Kudu, the battle of Wenjiang made him understand that the cavalry was just a target in front of the artillery in formation, of course, even if he had the idea of charging into battle, Kudu would never agree. The reason why Liu Heima let Kudu come was just to cover the retreat of his Mongol and Han army. For the past few days, the defenders of the city have been in a state of panic, and no one knows when the shells will come or who will be smashed into pulp, which has caused the morale of the defenders to fall to the bottom. What's worse is that the walls of the west gate, the north gate, and the south gate have been blown down for a while, and the artillery of the Thunderbolt army is still bombarding the defenders who are trying to close the gap, apparently preparing for the invasion of the city. Liu Heima understands that if he can't fight back just by being beaten, the city will definitely not be able to hold it, and he has to stop the loss in time before the situation can be managed.