Ultrasonic　surface　rolling　(USR),　carburizing　and　the　combined　(Carburizing　+　USR)　strengthening　method　were　applied　on　the　20CrMoH　steel,　and　the　rolling　contact　fatigue　(RCF)　mechanisms　of　20CrMoH　steel　subjected　to　different　strengthening　methods　are　analyzed.　Results　indicated　that　the　combined　strengthening　method　effectively　increased　the　surface　hardness　value　from　370　HV0.2　to　900　HV0.2,　produced　the　highest　residual　compressive　stress　(RCS)　value　of　-920　MPa　and　markedly　reduced　the　surface　roughness　value　to　0.48　mu　m.　Under　the　Hertz　contact　stress　of　2.02　GPa,　the　RCF　life　of　the　combined　treated　samples　increased　by　100%　compared　to　the　carburized　samples,　and　the　delamination　mainly　occurred.　Surface　roughness　and　RCS　are　important　factors　for　anti-RCF　failure.