Based on the macrofeatures and microfeatures of the outcrop sections and the drilling cores of the Leikoupo Formation of Middle Triassic in the northwest Sichuan Basin, and combined with the conventional petrophysical properties, this paper profoundly studies the basic features of the reservoir space types, petrographic and petrophysical properties, vertical distribution, as well as the main  factors controlling sedimentation and diagenesis. Furthermore, it discusses the development and evolution of main reservoirs and predicts the favorable reservoir distribution area. The reservoir concentrates in the middle part of member 3 of the Leikoupo Formation, where the rock types are mainly the sandsized intraclastic dolostone, algaebounding dolostone and macrocrystalline dolostone. The corrosion pore is predominant, while the dissolved cavity and primary pores are subordinate. The fractures play a role in  connecting the pores. The reservoirs are of the pore type of moderate porosity and moderatelower permeability, and the fracturepore type of moderate porosity and high permeability. Study shows that the reservoir is a karst reservoir in which pores are dominated by intergranular dissolved pores, algaebounding  framework dissolved pores and intercrystalline dissolved pores. The original rocks laid down as the intraclast bank and algaebounding  grain bank have experienced  karsting during the  hypergenic and burial stages. The reservoir resulted from the interactive influence of sedimentation and diagenesis. The favorable reservoir is distributed in the ZhongbaShuangyushi block, which is the superimposed area of the bank and karst development zone.