Abstract：The oolitic shoal reservoir in the Feixianguan Formation in the northeastern Sichuan basin, which has undergone strong diagenesis, is an important exploration target in the Sichuan basin. On the basis of an integrated analysis of all kinds of data, such as the core, common thin sections, mold thin sections, cathodoluminescence images, carbon and oxygen isotopes, trace elements and fluid inclusions, the paper deals with the main type, mechanism and product of diagenesis and analyzes the effects of diagenesis on the reservoir. Cementation and compaction were the leading destroyers of primary pores and part of secondary pores. Mixed-water dolomitization, corrosion (karstification) and rupturing were the leading builders of secondary pores and the solution pores, solution cavities and fractures produced by them are the dominant accumulation spaces and migration passageways for gas. The physical properties of the reservoir are mainly controlled by diagenesis, which controlled the evolution of pores.