In　order　to　improve　the　bearing　capacity　and　transmission　efficiency　of　planetary　roller　screw　mechanism　(PRSM),　comprehensively　considering　the　stiffness　of　the　shaft　section,　contact　stiffness,　and　thread　stiffness,　the　thread　load　distribution　model　of　PRSM　is　established　by　means　of　equivalent　spring.　The　numerical　solutions　of　deformation,　thread　stiffness,　and　thread　load　are　obtained　by　direct　stiffness　method,　and　the　calculation　results　are　verified　by　comparing　with　the　finite　element　results.　A　multi-objective　optimization　model　considering　deformation,　thread　stiffness,　thread　load,　and　transmission　efficiency　is　established.　The　optimal　solution　is　obtained　by　using　the　elitist　non-dominated　sorting　GA　(NSGA-II).　The　results　show　that　compared　with　the　one　before　optimizing,　the　overall　deformation　of　PRSM　is　reduced　by　about　10%,　the　thread　load　distribution　of　the　roller　on　the　screw　side　is　reduced　by　about　13.75%,　the　transmission　efficiency　is　increased　by　about　45%,　the　thread　stiffness　of　the　screw　is　increased　by　about　45%,　the　thread　stiffness　of　the　nut　is　increased　by　about　50%,　and　the　roller　thread　stiffness　is　increased　by　about　50%.　The　reliability　of　PRSM　is　significantly　improved.