Continuous　gas　leakage　paths　of　cement　sheath　during　hydraulic　fracturing　were　investigated　in　this　study.　The　finite-element　models　of　a　casing-cement-sheath-formation　assembly　for　the　whole　wellbore　were　established,　the　integrity　of　the　cement　sheath　of　the　whole　wellbore　during　single-stage　fracturing　was　analyzed　firstly,　and　the　factors　affecting　the　integrity　were　examined.　Furthermore,　a　cyclic　compression　test　was　conducted.　Then,　test　results　for　the　accumulative　plastic　strain　of　the　cement　sheath　under　the　intermediate　casing　shoe　during　multistage　fracturing　were　analyzed.　Finally,　the　mechanism　of　dilatancy　of　cement　stone　in　cyclic　compression　tests　was　analyzed.　The　results　show　that　the　radial　and　tangential　stresses　of　the　cement　sheath　increase　and　decrease,　respectively,　with　depth.　The　cement　sheath　above　the　intermediate　casing　shoe　had　a　risk　of　tensile　failure,　which　could　result　in　tangential　tensile　cracks.　The　cement　sheath　below　the　intermediate　casing　shoes　had　cumulative　plastic　strain,　resulting　in　a　microannulus.　Reducing　Young＇s　modulus,　increasing　the　Poisson　ratio　of　the　cement　sheath,　and　reducing　the　pump　pressure　were　beneficial　to　relieve　the　stress　state.　When　the　cyclic　compressive　stress　exceeded　the　dilatation　yield　stress,　the　permeability　increased　with　cycle　numbers,　and　the　increase　in　permeability　provided　another　leakage　path　for　gas　migration.