In the 16th year of Chongzhen in Ming Dynasty (1643), Emperor Taizong of Qing Dynasty died in August, and his son Fu Lin ascended the throne, who was the ancestor of Qing Dynasty. When Fu Lin was young, he was assisted by his uncle Dourgen. At the beginning of April in the seventeenth year of Chongzhen, Fan Wencheng, a great scholar in the Qing Dynasty, adopted the policy of "competing for the Central Plains". On April 7, the Qing court was full, and the Mongols almost rushed out, led by Regent Dourgen. This time, the marching route of the Qing army still adopted the route of invading the Ming Dynasty in the past, that is, bypassing Shanhaiguan and invading from the Great Wall. On April 15, after the Qing army entered Wenghou (near Fuxin, Liaoning), it received a letter from Wu Sangui, the company commander of Liaodong guarding Shanhaiguan, and immediately diverted to enter the customs. Shanhaiguan, facing the sea and facing the mountain, is an important pass east of the Great Wall in Wan Li in the Ming Dynasty, and has always been a battleground for military strategists. Wu Sangui, the company commander of Liaodong in the late Ming Dynasty, was named Pingxibo. When the Li Zicheng Rebels invaded Beijing, he led the elite into the customs. Li Baicheng had surrendered to him and refused, and fierce fighting took place between the two sides. On April 21st, the seventeenth year of Chongzhen, several dry cavalry of the rebel army advanced on Xiluocheng of Shanhaiguan, and the Amin army in the north wing revolted and surrendered to Li Baicheng, and Shanhaiguan City was just around the corner. On April 22nd, the Qing army galloped to Shanhaiguan, and Wu Sangui cut in line. With the joint efforts of Wu Ergui and the Qing army, the rebels in Li Zicheng were outnumbered and had to retreat, so the gate of Shanhaiguan was opened and the Qing army entered the Central Plains in large numbers. Soon, the Qing dynasty replaced the rule of the Ming dynasty.