The Eighth Route Army cooperated with Kuomintang troops to fight against the Japanese at Xinkou.

　　The Xinkou operation started to unfold on October 11, 1937 and came to a sudden end on November 2, lasting 23 days.

　　After the "Lugou Bridge (also known as the Marco Polo Bridge) Incident", the main force of the Japanese aggressors entered Shanxi Province from Hebei Province, and intended to attack and occupy Taiyuan City-the capital of Shanxi Province. Xinkou was the important gateway of north Shanxi to Taiyuan City and also the last defensive line for Taiyuan City. The Communist Party of China and the Kuomintang decided to join hands to launch a mass campaign to deal a head-on blow to the Japanese agrressors.

　　The Chinese troops started to engage the Japanese troops at the daybreak of October 11. The Japanese troops met with the unexpected resistance, then they threw in all kinds of heavy weapons to pound the Chinese troops' positions in the hope of achieving a quick victory but of no avail. In the following days, the two sides were locked in a seesaw battle and both suffered heavy casualties.

　　The Japanese troops attacked and occupied the Niangziguan Pass and then drove into the east part of Shanxi Province. Taiyuan signalled for help. The Chinese troops defending Xinkou took an initiative to pulled out on November 2 in order to help to defend Taiyuan City, hence winding up the Xinkou operation.

　　To cooperate with friendly-forces in fighting the Japanese aggressors, the Eighth Route Army ordered its No. 115 and No. 120 divisions to penetrate into the enemy's flanks and rear, and advanced towards Lingqiu, Guangling, Daixian, Guoxian and Yanmenguan to carry out guerrilla warfare for the sake of harassing and attacking the enemy from its rear. They recovered over 10 county seats, cut off the enemy's communication lines, destroyed Japanese airport at Yangmingbao, and weakened the Japanese air-strike capability considerably as result of damaging 24 Japanese aircraft and killing over 100 Japanese troops, thus supporting friendly-forces in front fighting at Xinkou.

　　During the Xinkou operation, the Japanese threw in more than 50,000 troops, of which over 20,000 were either killed or wounded, making the Xinkou operation the most fierce and longest operation with heaviest casualties of both parties in north China battlefield in the early stage of the War of Resistance Against Japanese Aggression. In order to turn the table, the Japanese changed its commander three times, but was of no help to the matter. Though the Chinese troops suffered setbacks in this operation and the following Taiyuan operation, it drained a lot of enemy troops, destroyed Japanese troops' operation plan in the Hebei Plain, gained time for the Chinese troops along the Beiping-Hankou railway line to withdraw to the south. Besides, it will go down in history as a typical operation jointly fought by the forces of the Kuomintang and the Communist Party of China.