Abstract: The dolomite of upper T2l4 of the Middle Triassic Leikoupo formation is thick and widely distributed in western Sichuan depression. High-yield industrial natural gas flows have been gained from the wells penetrated in the dolomite. Based on the analysis of cores and thin sections and combining with experimental test data, the paper studies the dolomitization in parasyngenetic and shallow-burial stages and discusses its impact on the reservoir development. The result shows that during the deposition period of upper T2l4 of Leikoupo formation, the study area was a restricted platform environment, the sedimentary water was shallow and the sea level changed frequently, dolomitized fluids were mainly seawater of the same period and thus very thick dolomite formed and were laterally distributed steadily; the dolomite stratum formed during the shallow-burial stage and before, dolomicrite, microcrystalline-powder crystalline subhedral-euhedral dolomite and a few powder-fine crystalline subhedral dolomite were found in the stratum. The geochemistry characteristics show that the dolomite formed in the early time; large amount of intercrystalline pores formed during the shallow-burial stage controlled dispersed flow of the corrosive fluids at the late stage, which resulted in the dolomite reservoirs dominated by laminated pore type or needle-like dissolved pore type in the study area