In　this　paper,　a　new　shock　model　is　proposed　to　fit　the　situation　that　the　damage　process　of　the　component　is　accelerated　with　the　increase　of　the　degree　of　damage　in　shock　environments.　Shocks　with　the　same　magnitude　may　have　more　serious　consequences　as　the　component　gets　worse　and　component　states　are　divided　into　different　stages　according　to　the　degree　of　damage.　Reliability　indexes　of　a　series　system　which　consists　of　two　components　with　the　above　characteristics　are　derived　by　using　a　Markov　renewal　process.　Then,　an　opportunistic　maintenance　strategy　is　proposed　for　the　system　and　an　optimization　model　is　constructed　to　obtain　the　optimal　maintenance　solutions.　Finally,　a　numerical　example　for　a　two-rolling　bearing　system　of　a　wind　turbine　is　presented　to　illustrate　the　proposed　shock　model　and　maintenance　strategy.　Sensitivity　analysis　of　maintenance　costs　is　also　discussed　in　order　to　improve　the　reliability　of　the　proposed　model.　This　study　is　of　reference　value　and　application　significance　for　similar　series　systems.