One　concern　to　rock　slopes　in　open　pit　mining　and　civil　engineering　is　the　potential　for　the　gradual　deformation　of　a　large　slope　to　develop　into　a　fast　moving　catastrophic　slide.　The　process　must　be　considered　as　a　potential　threat　where　large　deforming　slopes　occur.　The　degradation　of　rock　mass　strength　is　a　factor　in　the　process.　In　this　paper,　through　the　fatigue　tests　of　moderately　weathered　sandstone　sampled　from　a　rock　slope,　the　S-N　curve　equation　of　rock　fatigue　strength　is　established　and　the　fatigue　degradation　of　rock　slopes　under　cyclic　loading　is　further　studied　by　finite　element　simulation.　The　results　show　that　fatigue　accumulation　damage　will　be　generated　in　rock　mass　of　slope　under　cyclic　loading.　The　geotechnical　parameters　and　slope　stability　factor　are　gradually　decreased　with　the　cyclic　fatigue　loading.　Consumption　of　slope　fatigue　life　is　not　sensitive　to　geotechnical　parameters　and　stability　factor　at　the　initial　stage　of　fatigue,　however,　at　the　later　stage　sensitivity　increases.　When　the　threshold　value　of　accumulation　of　fatigue　damage　is　achieved,　the　rock　slope　failure　occurs　abruptly.