Due　to　insufficient　cement　return　height　during　cementing　operations,　there　may　be　a　channel　for　oil　and　gas　leakage　between　the　wellbore　and　the　formation,　causing　environmental　problems　such　as　groundwater　pollution.　Therefore,　it　is　necessary　to　reinject　the　cement　slurry　into　the　original　wellbore　annulus　and　evaluate　the　sealing　performance　of　the　remedial　cement　sheath.　However,　the　current　theoretical　and　applied　research　on　this　aspect　is　relatively　lacking.　In　response　to　this,　a　new　model　for　calculating　elastoplastic　strain　of　the　remedial　cement　sheath/original　cement　sheath　based　on　damage　mechanics　was　established,　and　the　plastic　deformation　behavior　of　the　interface　area　was　studied.　The　seal　failure　mechanism　of　the　wellbore　remedial　cement　sheath　is　clarified,　and　the　influence　of　the　mechanical　parameters　of　the　remedial　cement　sheath　on　the　cumulative　plastic　strain　and　the　micro-annulus　of　the　remedial　cement　sheath-casing　interface　is　analyzed.　The　results　show　that　under　the　combined　action　of　the　internal　pressure　of　the　casing　and　the　non-uniform　ground　stress,　the　cumulative　plastic　deformation　of　the　inner　wall　of　the　remedial　cement　sheath　and　the　micro-annular　gap　at　the　interface　are　the　main　reasons　for　the　sealing　failure　of　the　remedial　cement　sheath.　Increasing　the　Poisson’s　ratio,　cohesion　strength　and　internal　friction　angle　of　the　remedial　cement　sheath　and　reducing　the　elastic　modulus　of　the　remedial　cement　sheath,　is　helpful　to　reduce　the　accumulated　plastic　strain　and　improve　the　sealing　performance　of　the　remedial　cement　sheath.　©　2023,　The　Author(s),　under　exclusive　license　to　Springer　Nature　Switzerland　AG.