The fluvial sand bodies are characterized by rapid lateral facies variation, weak continuity and connectivity and strong reservoir heterogeneity, which seriously affect the development of the fluvial reservoir. Based on the study of the reservoir sedimentology, the fluvial sand bodies distribution and evolution of He 8 member in Su 14 block were studied. The result shows that the sedimentary background in the He 8 member is gradual transition from the early braided river deposition to the later meandering river deposition, and the sedimentary microfacies mainly includes channel lag deposits, channel bars, point bars, crevasse splays, natural levees, overbank sand and mud deposits. By the influence of the interaction between the base level and the sediment supply, the fluvial evolution experienced three stages, which are the braided river prosperous development stage, the braided river and meandering river coexistence and transforming stage and the meandering river prosperous development stage. The sand bodies of channel bar and point bar in the stage of the braided river prosperous development and the braided river and meandering river coexistence and transforming are the main gas-bearing reservoirs. The development of favorable gas-bearing sand bodies is controlled by sedimentary microfacies and base level cycles.