Underground Gas Storages (UGS) are widely used to store the surplus of produced natural gas during periods of low demand, and to relieve the pressure during periods of high demand. A depleted natural gas reservoir is generally the ideal choice for the UGS. The proper selection of a depleted gas reservoir is essential to the stability of the UGS in the long run. The storage ability is an important index for the performance of the gas storage. In order to analysis the stability of the storage ability of the UGS in BZ area, the development characteristics of the main reservoir are studied, with the pressure strain data of the reservoir analyzed and compared. The effect of the pressure strain on the porosity is evaluated by using mathematical formulas, and it is believed that the original porosity and the operation pressure are related with the effect of the pressure strain on the UGS. The case production history fitting of the gas storage has verified the analytical method and the mathematical chart board, which may offer an accurate and quantitative analysis of the storage ability in the UGS, and provide an analytical tool in the practical production management.