Abstract：Good reservoirs are developed in the Middle Triassic Leikoupo-43 Formation in Longgang-Yingshan area of central Sichuan basin. There exist rich oil and gas resources in granular dolomite, suggesting good exploration prospect. Through macro- and micro- observation of thin sections and rocks from more than ten wells in combination with geochemical characteristics, the authors made a detailed investigation into diagenetic types and characteristics and examined the relationship between the diagenesis and the evolution of reservoir space. The findings show that the diagenetic evolution process of reservoir in the Middle Triassic Leikoupo-43 Formation in Longgang-Yingshan area of central Sichuan basin was complex, and during this process various diagenetic actions were developed, with the reservoir quality being clearly affected by the diagenesis．The compaction and pressure solution, multiphase cementation and multiphase packing action resulted in substantial reduction of intergranular pores and intercrystalline pores. The mixed water dolomitization, the supergene and burial dissolution and the tectonic disruption constituted the keys to the formation of high quality reservoir and the generation of massive intergranular dissolution pores，intragranular dissolution pores, intercrystalline dissolved pores and eroded fissures, which have now became the main oil and gas reservoir space.