Abstract: Overpressure in Shahejie formation of Kuihuadao structure was occurred in the end of deposition of Dongying formation. Closed faults were the first condition for occurrence of overpressure, and continuous accumulation of gas was the important factor for overpressure. And fast deposition of sediments, dehydration of clay minerals and heat pressureboosting also had some contribution to the abnormal formation pressure.