Abstract:Hightemperatureflexuralstrengthofporoussiliconnitrideceramics(nolessthan50% porosity)undervacuumconditionswasstudied,andthephasesafterhightemperaturestrengthtestingwasanalysedalso.Theresultsshowthattheflexuralstrengthofporoussiliconnitrideceramicsisnegativelyrelatedwithtemperatureundervacuumcondition.Thesofteningofglassyphaseongrainboundaryunderhightemperatureisthemainfactorinfluencingthestrengthdecrease.