Abstract: Gas storage capacity and working gas volume are key issues in the construction of gas storage, the working gas volumes are in mutual limitation with operating pressure of gas storage, cushion gas volume and injection and production wells. Pressure drop method, flowing medium balance method and yield instability analysis method of calculating dynamic reserves are discussed. Evaluation on the storage capacity in southern district of Yulin Gasfield is made. The results show that the ratio of working gas volume to storage capacity gas is 27.5% with gas reservoir engineering method, and 25%～30% with the combination of multi-parameter optimization of the gas reservoir engineering and core injection and production simulation experiments, and integrated together with the evaluation results, the optimal working gas volume of the gas storage capacity is at 25% to 30%.