Abstract: Overpressure is widely developed in the Xihu Sag. The cost for a well in overpressure formation is obviously higher than that in normal pressure formation. Therefore, pre-drilling pressure prediction is a technique urgently required to enhance the accuracy of pressure forecasting, ensure drilling safety, and reduce drilling cost. After a careful review of historical cases, it is found that lower pressure calculation parameters and inappropriate calculation models are the reasons leading to the forecasting error.In this paper, a suit of new pre-drilling pressure prediction methods,such as the optimal Bowers calculation model using empirical coefficient for correction,is proposed upon the assumption that the overpressure is caused by organic process of hydrocarbon generation. The application of the methods is proven effective in the Xihu Sag.