Wu Sangui's clearance is full of doubts. On March 19, the seventeenth year of Chongzhen in Ming Dynasty (A.D. 1644), a peasant uprising army led by Li Zicheng captured Beijing under the rule of Ming Dynasty, and Chongzhen hanged himself in Jingshan Park. Wu Sangui, the company commander of Mingshan Shanhaiguan, heard the news and fled back to Shanhaiguan during the reinforcement. Li Zicheng led the army to Shanhaiguan and tried to force Wu Sangui to surrender by force. Wu Sangui was so scared that he turned to the Qing Dynasty for help. When the two armies of Li and Wu fought bloody battles in front of Shanhaiguan, the elite of the Qing army suddenly came out of the mountain, and the peasant army was unprepared and defeated, and it never recovered. Due to various records in historical books, historians have been paying attention to the incident that Wu Sangui led the Qing army into the customs to suppress the peasant uprising. People always thought that Wu Sangui's move was a surrender to the Qing Dynasty. However, in recent years, some people think that Wu Sangui's introduction of the Qing army into the customs does not mean that he surrendered to the Qing Dynasty, and various evidences have been presented. This statement makes the seemingly conclusive problem once again a historical mystery. Wu Sangui surrendered to the Qing Dynasty for at least two reasons: First, the supreme ruler of the Qing Dynasty regarded Wu Sangui as surrender. For example, Regent Dourgen of the Qing Dynasty took Wu Sangui as his subordinate, "ordered the soldiers of Sangui to wear white cloth as the number", "commanded the pioneers" and "commanded Wu Sangui to chase thieves with 20,000 pioneers". In order to reward Wu Sangui's contribution in the war, the Qing court also "awarded the Western King Sangui Pingxi" (Biography of Wu Sheng). Later, when the Qing emperor deprived Wu Sangui of his title, he also called it surrender: "The traitor Wu Sangui came back from poverty. My ancestor Zhang Ji remembered that he had been defeated and did not surrender, and gave him an army." In the eyes of the Qing court, Wu Sangui was a surrenderer of the Ming Dynasty. Second, Wu Sangui's actions after his entry into the customs also showed that he was sincere in settling the Qing Dynasty, and Wu Sangui lured the Qing Dynasty into the customs under the banner of revenge for the Ming Dynasty. However, when the axe king of Nanming regime sent people to Wu Sangui for many times, Wu Sangui flatly refused. For example, when Assistant Minister Zuo "paid tribute to Sangui and gave silver to make it a blessing", Wu Sangui said, "How dare I be given this, but I have to be tied behind closed doors and wait for my life" (Collection of Ming History). In addition to the axe king, there are several Nanming kings, and Wu Sangui never said that he would cooperate with the anti-Qing dynasty to regain his sight. On the contrary, he personally sent troops to Myanmar to assassinate King Li Yong of Nanming. It can be seen that no matter what Wu Sangui thought when he led the Qing soldiers into the customs, he surrendered to the Qing Dynasty after the Qing soldiers entered the customs. At this time, he didn't dare to disobey the orders of the Qing court, or even dare to have any idea of anti-Qing and regaining sight. In order to show his loyalty to the Qing dynasty, he "broke the thief, settled Shaanxi, settled Sichuan and Yunnan, took the king of Nanming in Myanmar, and settled the Tusi of Western Anshi" (Wu Shengji), which became a sword for the Qing court to pacify the world. Those who deny Wu Sangui's "surrender to the Qing Dynasty" believe that after the fall of Beijing, three powerful political forces coexisted, namely Wu Sangui, the peasant army and the Qing Dynasty. Wu Sangui, sandwiched between these two forces, is the weakest, so there are only two ways he can take: either resisting the Qing Dynasty or suppressing the peasant army. Considering that his father was detained by the peasant army and his wife was humiliated, Wu Sangui chose the road of uniting with the Qing Dynasty to avenge this, but this did not mean that he surrendered to the Qing Dynasty. The main reasons are as follows: First, Wu Sangui's consistent anti-Qing attitude determines that he will not settle down easily. During his tenure as company commander in Ningyuan, Liaodong, Wu Sangui participated in the anti-Qing struggle many times. Even after the war of Jinsong in Ming and Qing Dynasties, when the Ming army was obviously at a disadvantage, his attitude remained firm. Wu Sangui's imperial edicts were all "disobedient". Second, Dourgen strengthened his control over Wu Sangui after the entry war, which can prove that Wu Sangui did not surrender. According to historical records, on the day of the victory of Shanhaiguan War, Dourgen played politics, made Wu Sangui king of the day and handed over 10,000 infantry to Wu Sangui. This shows that Wu Sangui was wooed and controlled by Dourgen. Third, the Shanhaiguan campaign published after the war proved that Shanhaiguan did not fall. The Qing army and Wu Sangui pursued a 56-point attack, and Wu Sangui put forward slogans such as "Zhou's life has not changed, Hande can be kind" and "Try Chixian to return to China, and it is still Zhujiazhi's orthodoxy". If Wu Sangui had fallen, he would not have published such a campaign, nor would the Qing court allow him to do so. Fourthly, after the Shanhaiguan War, Wu Sangui's attempt to Prince Zhu Ming before and after the capture of Beijing proved that he did not surrender. Li Zicheng was defeated by Yongping, and Wu Sangui put forward that "I will return to the army, get out of the capital quickly, and make the Crown Prince the throne", and put forward that "the soldiers will enter the city in a few days, and all the ministers will mourn the first emperor and prepare for the East Palace", but the strategy of "Dourgen ordered him to go west to chase thieves" disrupted Wu Sangui's wishful thinking. Wu Sangui is too weak to listen to Dourgen. Fifth, the secret accumulation of strength to fight against the Qing Dynasty and regain sight can also prove that Wu Sangui has not fallen. While recruiting talents, he secretly spread his followers, "keeping the world healthy and forbearing the wizards of Jingchu", and at the same time "raising money" for future wars. The reason why he didn't realize his desire to fight against the Qing Dynasty and regain his sight was that the increasingly powerful political rule of the Qing Dynasty made the banner of "fighting against the Qing Dynasty and regaining his sight" lose its appeal. However, the historical question of whether Wu Sangui was purged can no longer be explained by the later historical process.