Abstract: Over one hundred meters of tidal-flat facies dolomite with dissolution-pores developed in the Middle Triassic Leikoupo Formation in the Longmen Mountain front in the western Sichuan Basin. It can be further divided into the upper and lower reservoirs. The analyses of well cores, debris, thin sections and physical properties show that the properties of the lower reservoir, dominated by superposed dolomites, are better than those in the upper reservoir, dominated by limestones. The reservoir formation mechanism was studied using SEM and inclusion homogenization temperature analyses based on rock physical property statistics and reservoir space characteristics. Dolomitization, dissolution in the penecontemporaneous period and dissolution during the burial period formed this good reservoir. Widely distributed dolomites, which developed in a tidal-flat facies, established an important foundation for a steady distribution of reservoirs, dissolution in the penecontemporaneous period determined the formation and distribution of good reservoirs, and dissolution in burial period was favorable for the retention of pores and the increase in permeability, further improving reservoir quality.