Casing is a weak part of underground gas storage during its operation period

which will be influenced by kinds of stochastic factors. In this paper

failure modes and failure criterions of casing and cement sheath are discussed firstly; then a three dimensional calculation model including casing

cement sheath and wall rock is established based on Jintan underground gas storage in Jiangshu province. Stochastic characters of geometrical size

load and material parameters of the casing system are analyzed

which are applied to the safety analysis. Then

failure probability and sensitive factors are calculated based on Monte Carlo method. At last

the simulation result is proved by a three dimensional geological model experiment. The research results indicate that the influences of the randomness responding to factors on casing reliability are different. Thickness of casing

inner diameter of casing

operation pressure and thickness of cement sheath are sensitive factors of casing-cement and wall rock system．Moreover

different factors have different effects on reliability. The reliability of casing decreases as storage pressure decreasing. And the reliability of cement sheath decreases as storage pressure increasing. More attention must be paid because failure probabilities of casing are high when the gas pressures of storage are extremely high or low. The gas extraction rates determined by the volume convergence law of the caverns will not influence the safety of casing-cement and wall rock system.