Abstract: It is difficult to find the deep exploration direction in the TJT structure area of the middle-south area of Baochu slope, Xihu Sag. This article describes various diagenetic phenomena in Pinghu Formation reservoir of the TJT structure from the conventional data of 5 existing wells, and analyzes the physical characteristics and vertical changes of the TJT structure reservoir. According to the data of formation water and salt water inclusions, this paper also discusses the possibility of deep secondary dissolution. Besides, The controlling facies machnism of oblique broom shaped fault terraces and the influence of eustatic cycle on the distribution of the reservoir are discovered, and then it is considered that the deep reservoirs in the lower Pinghu Formation are mainly lithologically formed.