Underground natural gas storage in depleted oil and gas reservoirs is an important part of the large-scale natural gas pipeline network, and ensuring its safe and reliable operation is especially important to guarantee the gas supply capacity of the pipeline network system. According to the process characteristics and the function zoning of the Underground Gas Storage (UGS), the process is separated into the gas injection process and gas production process, and the function zoning is divided into reservoir, wells system containing multiple injection/production wells and surface system. In this paper, through the wells system, the reservoir and surface system are connected, and the operating reliability of Underground Gas Storage (UGS) under required gas injection and production tasks is calculated based on the integration method. Finally, the actual data of an underground natural gas storage is used to evaluate its operating reliability.