Abstract: In the process of pressurization by injecting gas in the wellbore of gas storage, the cement sheath suffers plastic deformation. And during unloading, micro-annular is produced, which leads to the seal failure of the wellbore. The elastic-plastic mechanics model for casing-cement sheath-stratum system was established using ABAQUS. Then, the change process of the gas pressure in the wellbore was simulated. Finally, combined with elastic modulus of cement sheath and stratum, the change laws of the matching relationship between casing-cement sheath-stratum in gas storages were analyzed. It is indicated that different types of casing can be matched with the optimal cement sheath thickness by taking no plastic strain in the cement sheath as the criterion and the internal pressure strength of the casing as the constraint. What's more, when the casing size is fixed, the smaller the elastic modulus of stratum and cement sheath, the thicker the cement sheath, the greater the casing pressure and the less possible the wellbore seal failure of gas storage.