Abstract: The oolitic beach carbonatite is the most important type of gas reservoir in the Lower Triassic Feixianguan formation in Northwestern Sichuan Province. The forming conditions of the beach facies reservoir of Feixianguan formation consist of mainly structure, sedimentation and lithogenesis. Analysis shows that the elevating movement caused by the contemporaneous faults controls the distribution of beach bodies. The beach bodies are easy to form and evolve on heaved side. The tableland of high energy sedimentary facies is favorable for the forming and evolving of reservoir. The oolitic beach that was reformed by intensive lithogenesis with dolomitization and dissolution would form fine reservoir.