Using the homogenization temperatures of brine inclusions formed in the same period as hydrocarbon inclusions, in combination with the burial and heat history, the authors got to know that the formation time of the natural gas reservoir of sandstone in 3rd and 4th Member of Denglouku Formation should be 96～81.5 Ma, which can be further divided into three periods, namely 93～91Ma, 88.8～82.8 Ma and 82 .3 Ma～81.5 Ma. The first two periods lasted relatively long, whereas the third period lasted comparatively short. According to the phenomena that the distribution of the secondary pores is controlled by T4 fault macroscopically and that there exists the development-underdevelopment-development cycle microscopically, it is held that fractures served as the migration pathways of the acid fluids. The formation time of early T4(the sedimentary time of Denglouku Formation, 1st Member of Qingshankou Formation and Yaojia Formation) was the time when the secondary pores were formed. The matching of the reservoir and the cover seemed to be most perfect in the sedimentary period of 1st Member of Qingshankou Formation, during which the formation time of the secondary pores and that of the injection of hydrocarbon matched well, resulting in the easy formation of gas reservoirs. The matching of the reservoir and the cover was relatively good in the sedimentary period of Yaojia Formation, however during which the gas source remained insufficient. In this period, the secondary pore belts could form low-yielded gas reservoirs or gas-water formations. The matching of the reservoir and the cover was the worst in the sedimentary period of Denglouku Formation, during which the secondary pore belts could hardly be preserved, leading eventually to the formation of dry formations.