On the sixth day of the seventh month, Zhu Yuanzhang personally led 200,000 sailors to rescue Hongdu. On the 16th, they arrived at the mouth of Jiangxi Lake.

First, he sent troops to defend the Jingjiang Estuary (now Susongnan, Anhui), and sent another army to Nanhuzui (northwest of present-day Hukou, Jiangxi) to cut off Chen Youliang's return route; He also sent troops to guard Wuyangdu (now east of Nanchang County, Jiangxi) to prevent Chen's army from escaping; Zhu Yuanzhang personally led the sailors from Songmen (now Changnan, Jiangxi) into Poyang Lake, forming a trend of closing the door and beating dogs.

Chen Youliang heard that Zhu Yuanzhang's army came to help, that is, he withdrew the siege of Hongdu and went east to Poyang Lake to face the battle. An unprecedentedly fierce and unusually fierce life-and-death battle unfolded on the surface of Poyang Lake.

On the 20th, the two armies met on the surface of the lake at Kanglang Mountain (now in Poyang Lake, Jiangxi). The giant ships of the Chen army joined forces and arranged the formation, spreading for dozens of miles, "looking at it like a mountain", and the momentum was overwhelming. Zhu Yuanzhang divided his own ships into 20 teams, each of which was equipped with large and small artillery, firearms, rockets, thistles, large and small muskets, magic arrows and bows, and ordered each team to fire firearms first, then use bows and crossbows when approaching the enemy ships, and then use short weapons to fight when approaching the enemy ships.

The next day, fierce fighting ensued between the two sides. Xu Da, the general of the Zhu army, took the lead and led the fleet to bravely attack, defeating the advance of the Chen army, killing 1,500 enemies and capturing a huge ship.

Yu Tonghai took advantage of the wind and fired cannons and burned more than 20 ships of Chen's army, and many of Chen's troops were killed and drowned.

However, Zhu's army also suffered a lot of casualties, especially Zhu Yuanzhang's ship ran aground and was surrounded, and he was in danger of being unexpected.

The battle was in a stalemate. From morning to dusk, the two sides closed their troops, and the battle came to an end, with casualties on both sides, regardless of victory or defeat.

On the 22nd, Zhu Yuanzhang personally led the sailors to battle. However, Chen's ship was huge, and Zhu's warship was too small to attack on its back, and it suffered setbacks one after another. At this time, Zhu Yuanzhang promptly adopted the suggestion of his subordinate general Guo Xing and decided to use fire to break the enemy instead.

At dusk, the northeast wind blew on the lake, and Zhu Yuanzhang chose brave soldiers to drive 7 fishing boats, which were filled with gunpowder and firewood, approaching the enemy ship, setting fire to the wind, and the wind was fierce and spread rapidly.

For a while, the flames soared, the lake was completely red, and in an instant, hundreds of huge ships of the Chen army were burned, more than half of the Chen army was killed and wounded, and Chen Youliang's two brothers and the general Chen Puluo were burned to death.

Zhu Yuanzhang took advantage of the situation to launch a fierce attack and killed more than 2,000 enemies.

On the 23rd, the two sides clashed again, and Chen Youliang saw Zhu Yuanzhang's flagship launch a fierce attack. As soon as Zhu Yuanzhang moved to his ship, the original ship was smashed by Chen Jun.

On the 24th, Yu Tonghai and others led 6 ships to break into Chen's fleet, galloping bravely, like a swimming dragon, like entering a no-man's land. The morale of the Zhu army was greatly boosted and a fierce attack was launched.

In the end, Chen's army was not defeated and retreated, and the abandoned drums and weapons were abandoned, and the lake was floated. Chen Youliang had no choice but to gather the remnants and turn to defense, not daring to fight again. In the evening of the same day, Zhu Yuanzhang took advantage of the victory to enter Zuoli (now northwest of Duchang, Jiangxi) to control the upper reaches of the river, and Chen Youliang also surrendered to Zhuji (now Xingzinan, Jiangxi).

The two armies held each other for three days, and Chen's army was defeated repeatedly, and the situation gradually became more and more unfavorable. Chen Youliang and the two generals saw that the general trend had gone, so they surrendered to Zhu Yuanzhang, and the internal morale of the Chen army was shaken, and the strength was even weakened.

Chen Youliang was angry and annoyed, and ordered all the captured captives to be killed to vent his anger. However, Zhu Yuanzhang did the opposite, returned all the prisoners, mourned the death and medical wounds, and broke the morale of Chen's army, thus winning the hearts of the people.

Chen's army was partially disintegrated, and morale was even lowered. Zhu Yuanzhang judged that Chen's army might break through and retreat into the Yangtze River, so he moved to the mouth of the lake, set up wooden fences on the north and south banks of the Yangtze River, placed large boats and rafts in the middle of the river, and sent troops to seize Qizhou and rejuvenate the country, control the upper reaches of the Yangtze River, block the enemy's return route, and wait for the opportunity to annihilate the enemy.

After more than a month of confrontation, Chen Youliang was trapped in the lake, running out of military food and exhausted. So he made a desperate bet and broke through at the risk of death.

On August 26, it broke through from Nanhuzui and attempted to enter the Yangtze River and retreat to Wuchang.

When they reached the mouth of Jiangxi Lake, the Zhu army attacked on all sides with boat divisions and fire rafts, Chen Jun could not advance, and re-walked the Jingjiang River, and was ambushed by Fu Youde, rushing left and right, unable to open a way out, Chen Youliang was killed by an arrow, the army was defeated, and more than 50,000 people surrendered.

The water battle, which began on 20 July and ended on 26 August, lasted 37 days.

The decisive battle ended with Zhu Yuanzhang's complete victory. The battle was regarded as the largest water battle in the medieval world.

It created a famous example of winning more with less in the history of China's water warfare, laid the foundation for the unification of Jiangnan, and created extremely favorable conditions for the later Northern Expedition and the defeat of the Yuan Dynasty and the unification of the whole country.