Just when the Yue army was attacking the Songhu area on a large scale, the offensive of the Yue army in North China never stopped. In the direction of the Pingsui Line, since the outbreak of the Battle of Nankou on August 8, our army was not afraid of sacrifice and desperately resisted the attack of the Yue army, inflicting great casualties on the Yue army. However, as Seishiro Itagaki's 5th Division joined the battle, the pressure on our troops gradually increased, and finally due to heavy casualties, they were forced to withdraw from the battle on August 26. On August 26, the Fifth Division occupied Huailai. On the 27th, the Chahar Corps led by Hideki Tojo sent a corps to occupy Yanqing, and Zhangjiakou, the capital of Chahar Province, fell.

After the fall of Zhangjiakou, Chahar sent the corps and the 5th Division of Seishiro Itagaki to continue to attack westward along the Pingsui Railway.

On August 28, Yan Xishan set up a camp in Taiheling, Dai County, and deployed to start the Battle of Datong with the Yue army. The troops participating in the battle included the 19th Army of Wang Jingguo of the Jin Sui Army, the 61st Army of Li Fuying, the 34th Army of Yang Chengyuan, the two brigades of Zhao Chengsui's Cavalry Army, the two infantry brigades of Fu Zuoyi's 35th Army, Chen Changjie's 72nd Division and Ma Yanshou Cavalry Brigade, and Liu Maoen's 15th Army of the Northwest Army.

After receiving the news, Jin Zhao discussed with the staff officers of the headquarters and decided to order Li Longbu to abandon the Chadong area, retreat to Suiyuan, and defend Suiyuan. There are two reasons that prompted Jin Zhao to decide to abandon Chadong, one is that once the Yan Ping Sui Line captures Suiyuan, then Chadong's Li Long Department will be surrounded by the Yue army on three sides, and the situation will be extremely dangerous. Of course, this is not the main reason, the main reason is that Jin Zhao and Fu Zuoyi cooperated, invested in Baotou to build a factory, after more than two years of development, the grassland steel city has begun to take shape, and now Baotou has become one of the important industrial towns in the north. Moreover, Jin Zhao and Fu Zuoyi built a secret arsenal in Baotou, which has now begun to take shape, although it is not as good as Yan Xishan's Taiyuan Arsenal, but it is not far behind. Fu Zuoyi's 35th Army and Li Long's 80th Army both relied entirely on the Baotou Arsenal for replenishment, and once Baotou fell, the blow to the 35th Army and the 80th Army would be very huge. In Jin Zhao's impression, in the original history, Baotou eventually fell. Therefore, in order to defend Baotou, Jin Zhao ordered Li Long to abandon Chadong and retreat to Ulanqab in Suiyuan. Of course, operations behind enemy lines were also quite important, so Jin Zhao still asked Li Long to leave a guerrilla force, appointed Huang Kang as the commander of the guerrilla column, and insisted on fighting behind enemy lines in the Chadong area.

On 1 September, the 5th Division of the Sakagaki Army and Hideki Tojo Chahar sent the vanguard of the corps with a total strength of 45,000 men, with the support of aircraft and tanks, to advance westward from Zhangjiakou and launch a fierce attack on the position of the 61st Army in Tianzhen through Huai'an.

Yan Xishan's deployment was to guard Tianzhen and Gaoyang with seven regiments of the 61st Army under Li Fuying, resolutely block the attack of the Yue Army, and use nine regiments of the 19th Army of Wang Jingguo to meet the 61st Army on the front line of Julebao east of Datong; Yang Chengyuan's 34th Army and Liu Maoen's 15th Army of the Northwest Army gathered in the area of Hunyuan and Dongjingji south of Datong to reinforce at any time; Two brigades of Zhao Chengsui's cavalry army were assembled on the Xinghe line north of Datong; With Fu Zuoyi, the 35th Army, a total of nine regiments, plus two cavalry brigades, a mountain artillery regiment, and a field artillery battalion were assembled in Dongfeng Town and the North Deshengbao area as the northern front corps. These three divisions were used as the receiving forces of the 19th Army and the 61st Army to assist in blocking the attack of the Japanese Army. Chen Changjie's 72nd Division, which broke through from Nankou, and the newly organized Fourth Brigade were organized into the First Reserve Army, with Chen Changjie as the commander, and assembled in Yingxian County, south of Datong. Sun Chu's 33rd Army, Meng Xianji's 8th Brigade and Zhang Zhengyu's 3rd Brigade were assembled between Longquan Pass and Pingxingguan as reserves. These two divisions were the general reserves of the entire Datong Battle.

This was the second Datong Defense Battle after the Datong Defense War launched by the Jin Sui Army with the Nationalist Army in 1926. Chiang Kai-shek was very interested in this operation, and hoped that the Jin Sui army, which was known for its good defense, would be able to create another victory in the defense of Datong in the face of the attack of the Yue army.

Li Fuying's 61st Army chose Tianzhen as the main battlefield, and placed six regiments in Tianzhen, and only one regiment in Gaoyang, in an attempt to inflict heavy casualties on the Yue army in Tianzhen, and then counterattack with Wang Jingguo's 19th Army and other follow-up troops. The 61st Army, commanded by Li Fuying, was reorganized from the 68th Division led by him before the Anti-Japanese War. Its strength is no more than one division. In terms of the strength of the enemy and us, the strength of the defender Li Fuying was far from that of the Yue army.

Li Fuying received Yan Xishan's order to "hold on for three days and resist the enemy's westward advance!" At that time, Li Fuying thought that it would not be a problem to hold on for three days with the strength of his own army, so he gladly accepted the order. But as soon as the battle began, Li Fuying knew that he had underestimated the strength of the Yue army, and the past three days were not so good.

The day after the officers and men of the 61st Army entered the position, the army launched an offensive. The army first rushed to the front of the position with a small force of infantry and fired fiercely, testing the firepower and tempting our defenders to take the initiative to expose their firepower. If it was Jin Zhao, a general like Li Long who had fought with the little devil, he would definitely see through the tricks of the little devil at a glance, but the officers and men of the 61st Army had no combat experience at all, and when they saw the army attacking, they shot back one after another! So much so that the firepower point was completely exposed, and at this time, the little devil Cang Queen withdrew. The officers and men of the 61st Army were excited, thinking that the little devils were just like that, running away as soon as they hit them, how did they know that the nightmare had just begun.

Soon the roar of a motor sounded in the sky, and the fighters of the army arrived. The army first bombed the mountains with planes at low altitudes, and then bombarded the mountains with artillery. This was bombed 4 or 5 times a day for 4 days and 4 nights. At its peak, there were 32 sorties a day that swept and bombed indiscriminately over the positions. Before the soldiers of both sides could officially meet each other, our defenders suffered heavy losses under the heavy artillery fire of the Japanese army.

Fortunately, although the 61st Army suffered heavy losses under the bombardment of the Yue Army, the infantry of the Yue Army did not launch a full-scale attack, and Li Fuying easily survived the first three days, but at this time he received a telegram from Yan Xishan, ordering the 61st Army to "continue to hold for 3 days and cover the Battle of Datong." Li Fuying had no choice but to accept his order.

But the next three days were even more difficult, and on the fifth day, the army launched a full-scale attack, with planes bombing in turn in the sky, roaring platoon artillery on the ground, and infantry rushing under the cover of tanks, and the enemy's attack power was very fierce. However, our officers and men of the 61st Army shared the same hatred for the enemy, fought tenaciously with a desperate spirit, and repelled the enemy's attacks and ...... again and again.