Abstract: The gas reservoir of Leikoupo43 sub?member of the Middle Triassic in Longgang area of central Sichuan basin has no uniform gas?water interface, and its late development is controlled by the complex gas?water relationship. Based on the analysis of the geochemical characteristics, the study on the gas and water distribution regularities reveals that the gas accumulation was controlled by the reservoir heterogeneity, sedimentary facies, tectonic setting, fault and fracture and preservation condition, etc. The comparative analysis of gas composition and isotopic characteristics indicates that the overlying Xujiahe formation is the main gas source layer of Leikoupo gas reservoir; In a certain condition of hydrocarbon generation intensity, the reservoir of grain shoal subfacies has good physical properties, with a high degree of gas charging. The gas layer, gas?water layer, gas?containing water layer are all dominated by isolated structural traps, the tectonic setting is of obvious differentiation effect on the gas and water; the developed faults and fractures in this area provide primary gas conduction system and reservoir space; the bottom mudstone of the Xujiahe formation and the Leikoupo gypsum?salt rocks constitute good conditions for hydrocarbon preservation