 Liu became a trusted general of Dou's, and was often in charge of making surprise attacks and conducting surveillance missions.Around the new year 620, Li Shiji further suggested to Dou that they should attack Cao () and Dai () Prefectures (together making up about modern Heze, Shandong), then controlled by the agrarian leader Meng Haigong () and nominally submitting to Zheng.Li Shiji was planning to ambush Dou as soon as he crossed the Yellow River, but Dou was delayed by Empress Cao's giving birth.