Abstract: According to the system reliability theory, and based on the research results of power system reliability, preliminary efforts are made in reliability evaluation of underground gas storage. In aspect of safe operation, reliability parameters of underground gas storage system are determined, including failure rate, reliability and availability, and corresponding calculation method is put forward. In aspect of user demand, reliability evaluation indexes of underground gas storage system are established, including gas deficiency time probability, gas deficiency time frequency, expected number of gas deficiency time, average duration of gas deficiency time, expected number of the gas deficiency capacity, index of gas deficiency capacity and influence degree index of cutting off gas, and corresponding calculation method is formed. Reliability level of underground gas storage system can be divided according to the influence degree index of cutting off gas, which provides a reference for decision-makers to make plan.