Abstract: Leakage, a serious problem, often occurs in the exhausted underground natural gas storage built around the city during its running period, which results in less actual reserves than that of account. Combining the methods of numerical simulation and parameter auto-fit, this paper dynamically confirms the pressure variation of the storage as the time. By adjusting the actual injecting-producing gas, it makes calculated and measured pressure fit well and then obtains the leakage of the storage. Finally, the actual reserves can be calculated through detracting leakage amount from accounted gas. The simulation results of the illustration show that the method presented can provides theoretic foundation to collating actual reserves, ensuring the leakage route, reducing leakage and improve injecting-producing rate by adjusting the storage method.