At first, Shi Siming served the Pinglu military envoy Wu Zhiyi as a general, and Wu Zhiyi was also very friendly to Shi Siming. Wu Zhiyi's son Wu Chengen was too shou for Xindu, and the county surrendered to Shi Siming, and Shi Siming saved him because of his old grace. When An Qingxu's army was defeated and fled back to Hebei, Wu Chengen persuaded Shi Siming to return to the imperial court. Li Guangbi thought that Shi Siming would rebel after all, and Wu Chengen was Shi Siming's cronies, so he let him secretly plot against Shi Siming. Li Guangbi also persuaded Suzong to appoint Wu Chengen as the deputy envoy of Fanyang Jiedu, and rewarded Ashina Chengqing Iron Coupons, so that they could jointly eliminate Shi Siming, and Suzong agreed.
Wu Chengen used his personal wealth to recruit soldiers many times, and repeatedly put on a woman's clothes and secretly went to the camps of other generals to lure the soldiers, and the generals secretly reported the matter to Shi Siming. Shi Siming suspected that the matter was not conclusive and did not pursue it. At this time, Wu Chengen entered Beijing, and Suzong sent the eunuch Li Sijing to Fanyang with him to comfort Shi Siming. After Wu Chengen announced the emperor's holy decree, Shi Siming left Wu Chengen to live in the mansion. And he covered his bed with a tent, and secretly sent two men to lie under the bed.
Wu Chengen's youngest son was in Fanyang, and Shi Siming asked him to visit his father. In the middle of the night, Wu Chengen whispered to his son: "I was ordered by the emperor to get rid of Shi Siming, a traitor, and appointed me as the envoy of the festival after the matter was completed. At this time, the two men who were lying under the bed cried out. So Shi Siming arrested Wu Chengen, searched his bags, and got the iron coupon and Li Guangbi's official document, which said: "If Ashina Chengqing can succeed, pay the iron coupon, otherwise don't pay him." He also found a book with hundreds of pieces of paper, which was a list of soldiers who had followed Shi Siming's rebellion before.
Shi Siming scolded Wu Chengen and said: "What am I sorry for you, you would do such a thing!" Wu Chengen thanked the sin and said: "I really deserve to die, this is all due to Li Guangbi's scheme." So Shi Siming summoned the soldiers and the people, and cried to the west: "I led 130,000 people to submit to the imperial court, what is there to be sorry for Your Majesty, and you want to kill me!" Then he beat Wu Chengen and his son to death with sticks, and more than 200 people were killed. Wu Chengen's younger brother Wu Chengxuan escaped to avoid death. Shi Siming imprisoned the eunuch Li Sijing and reported the matter to the imperial court. The eunuch sent by the Su sect comforted Shi Siming and said: "This is not the intention of the imperial court and Li Guangbi, it was all done by Wu Chengen alone, and he deserved to kill him."
Although Shi Siming accepted the appeasement of the imperial court on the surface, the seeds of rebellion had been planted in his heart. He began to secretly contact the old troops, regrouping his forces, and at the same time strengthening his control over Fan Yang. He knew that in order to truly become the overlord of the north, he must first stabilize his own territory. 