In recent years, multiple exploration breakthroughs have been made in the Third Member of the Leikoupo Formation in the Middle Triassic of Northwest Sichuan Basin. Currently, the overall exploration level is low. The characteristics and formation mechanism of the reservoir are unclear. Techniques such as core observation, pore permeability testing, conventional and cast thin section identification, scanning electron microscopy, mercury intrusion and nuclear magnetic resonance were used to clarify the sedimentary and reservoir characteristics of the 2nd section of the Maokou Formation in the front of the Longmen Mountains in western Sichuan and to explore the main controlling factors of high-quality reservoirs. Research shows that the reservoir rock types are mainly granular dolomite, microbial dolomite and icro-crystalline dolomite. The storage spaces are mainly composed of secondary dissolved pores such as intergranular dissolved pores, microbial "frame" dissolved pores and intercrystalline dissolved pores. The overall physical properties are relatively dense, belonging to medium-low porosity and low permeability reservoirs, with an average porosity of 2.78% and an average permeability of 0.76 mD. Sedimentary facies, diagenesis, paleogeomorphology and tectogenesis jointly control the development of the T₂l₃ member reservoir in northwestern Sichuan basin. The development of reservoirs is controlled by sedimentary facies, ancient landforms, and diagenesis. The material basis for the development of favorable reservoirs is formed by the deposition of high-energy sand and debris shoals, biogenic debris shoals. The surface dissolution effect of karst slopes in ancient landforms is the best. The quasi contemporaneous dolomitization, recrystallization, and multi-stage karstification are the key factors for reservoir development. Structural fractures and faults are favorable conditions for reservoir improvement. The Zhongba area and the southwestern part of the Shuangyushi area are located at the intersection of high energy beaches and karst slopes with micro ancient landforms. The thickness of the dolomite is large, with developed faults and fractures, strong dissolution, and the development of Class I and II reservoirs. They can be used as key exploration targets for the next step.