The thick Sinian Dengying marine dolostone karst reservoir overlaid by Middle Cambrian evaporate rock is the important target of exploration in the western Hubei-eastern Chongqing area. Two episodes of tectonic uplifting and karstification related with Tongwan movement occurred in this area, which brought in one and two fracture-cave zones respectively in the upper and middle parts of Dengying Formation. These fracture-cave zones are dominantly filled with regular chemical precipitation, including the fillings of micritic dolomite, dolomicrite, fine-coarse crystalline dolomite in the upper part and the fillings of micritic dolomite, dolomicrite, nematodolomite and granular dolomite in the middle part. It is indicated that the development of fillings is influenced by flowing paths and rates of the leakin g saturated carbonate fluid, and the residual secondary pores provide space for the present reservoirs.