This　study　used　the　strength　reduction　method　to　analyze　the　seismic　stability　of　a　subsea　tunnel　under　the　effects　of　seepage　and　temperature.　Excess　pore　water　pressure　within　the　rock　mass　was　first　eliminated　by　calculating　the　consolidation;　then,　an　earthquake　wave　was　applied　to　begin　the　dynamic　and　time-history　analysis　and　to　obtain　the　maximum　horizontal　displacement　of　the　model　boundary.　Finally,　a　temperature　field　model　was　established　for　the　thermal　analysis　of　the　structure.　The　temperature　of　each　node　of　the　structure　was　regarded　as　a　form　of　outside　load　applied　to　the　reduction　model;　both　sides　of　the　vertical　horizontal　displacement　of　the　boundary　nodes　and　gravity　were　used　as　inputs　for　the　static　analysis　when　the　vertex　horizontal　displacement　reached　its　maximum　value.　By　continuously　decreasing　the　shear　strength　parameters,　the　safety　factor　of　the　tunnel　structure　was　determined.　The　results　show　that　the　plastic　zone　first　appeared　in　a　smaller　range　on　both　sides　of　the　tunnel　arch　feet　near　the　lining　and　vault　of　both　sides.　The　safety　factor　decreased　with　increasing　water　depth　and　overburden　layer　thickness.