Abstract: As the main exploration target in WBT Area of Xihu Sag, the Lower Pinghu Formaiton was investigated.By analyzing the characteristics of lithology, reservoir space and physical property, the favorable controlling factors of reservoir quality were summarized. On this basis, the maps of sedimentary facies, diagenetic facies and pressure coefficient distribution were overlapped to fix the distribution area for favorable reservoirs. And the result shows that lithology of the Lower Pinghu Formation is mainly feldspar lithic sandstone. The reservoir space is mainly secondary dissolution pores, but a large number of primary pores are still retained. The distribution characteristic of the reservoir is controlled by sedimentary facies and diagenesis has a great effect on primary pores, which is also protected by the abnormal high pressure. It is predicted that the down thrown block of WB Fault and BT Fault and the western WB Area are I and II favorable reservoir regions.