A set of layer-liked karstic dolostone reservoir asa weathering crust develops at the top bed of Middle Triassic Leikoupo4 Member (Lei 43) in Longgang area, Sichuan Basin. The epidiagenetic weathering crust palaeokarst is dominant in the palaeokarstication. By the affection of the palaeogeologic setting and lithologic association, the palaeokarst is characteristic of the short-time and weak dissolution, and strong filling and anhydrite decomposition. It is shown that the palaeokarstification of weathering crust is the key factor in development of the reservoir, which plays actions of not only construction but also destruction for the reservoir.