Liu Heita
Qin then followed Li Shimin in defeating Liu's major general Song Jin'gang (), contributing to Li Shimin's final victory over Liu later in 620. Emperor Gaozu awarded Qin with a large supply of gold and silk. Later that year, Li Shimin launched a major attack against Wang, who by this point had deposed Yang Tong and declared himself emperor of a new state of Zheng. During the campaign, Li Shimin selected some 1,000 elite soldiers, clad in black uniform and black armor, commanded by Li Shimin himself, to serve as the forward advance corps, with Qin, Cheng Zhijie, Yuchi (who by this point had surrendered to Tang), and Zhai Zhangsun () as his assistants. This corps subsequently accomplished much during the campaign against Wang and Dou Jiande the Prince of Xia, who came to Wang's aid. During initial engagement against Xia troops, Qin, Yuchi, and Li Shiji were able to defeat Xia forward troops, and Li Shimin subsequently wrote Dou, citing the battle as a reason why he should stop his campaign to aid Wang. Dou did not relent, and in summer 621, his and Li Shimin's troops engaged at the Battle of Hulao. Qin contributed much during the battle, which ended with Dou's being captured by Tang forces. Wang subsequently surrendered, and both Zheng and Xia territory were seized by Tang (although later that year Dou's general Liu Heita rose against Tang rule and briefly recaptured nearly all of Xia territory). For his achievements against Zheng and Xia forces, Qin was created the Duke of Yi. In 622, he also followed Li Shimin in fighting against Liu Heita.