This　study　focused　on　the　sealing　failure　mechanism　and　control　method　for　a　cement　sheath　during　hydraulic　fracturing.　Taking　a　shale　gas　well　as　an　example,　whole　wellbore　numerical　models　of　the　casing-cement　sheath-formation　assembly　were　established,　failure　modes　of　the　cement　sheath　at　different　depths　were　clarified,　and　control　methods　were　proposed　based　on　the　calculation　results.　The　following　conclusions　were　drawn.　(1)　The　maximum　radial/tangential　stress　of　the　cement　sheath　increased/decreased　with　an　increase　in　the　depth,　and　the　cement　sheath　above　the　intermediate　casing　shoe　posed　the　risk　of　tangential　tensile　failure,　resulting　in　tensile　cracks.　The　cement　sheath　below　the　intermediate　casing　shoe　produced　a　micro-annulus　under　a　cyclic　casing　pressure,　and　the　tensile　cracks　and　micro-annulus　constituted　passages　for　the　sustained　casing　pressure.　(2)　The　swelling　stress　of　the　expansion　cement　slurry　could　offset　the　circumferential　tensile　stress　and　increase　the　radial　compressive　stress.　Because　a　cement　sheath　with　a　high　Young＇s　modulus　usually　exhibits　high　tensile　and　compressive　strengths,　it　is　recommended　to　use　a　high　Young＇s　modulus　cement　slurry　system　above　the　intermediate　casing　shoe　and　optimize　the　free　expansion　ratio.　(3)　In　comparison　with　ordinary　cement　stone,　low　residual　strain　cement　stone　exhibited　a　larger　elastic　deformation　interval.　The　cumulative　residual　strain　caused　by　cyclic　loading　was　smaller,　and　the　Young＇s　modulus　demonstrated　a　lesser　decrease.　The　results　of　an　equivalent　physical　experiment　demonstrated　that　an　ordinary　cement　sheath　lost　its　integrity　after　13　loading　cycles　with　a　maximum　casing　pressure　of　60　MPa.　A　low　residual　strain　cement　sheath　could　guarantee　integrity　after　30　loading　cycles　when　the　maximum　casing　pressure　was　90　MPa,　and　sealing　failure　occurred　after　11　loading　cycles　when　the　maximum　casing　pressure　was　130　MPa.　It　is　recommended　to　use　a　low　residual　strain　cement　slurry　below　the　intermediate　casing　shoe　to　prevent　a　microannulus.