Many　production　systems　undergo　a　multistate　deterioration　process　before　failure,　during　which　inspection　and　repair　are　used　to　detect　and　remove　the　defects.　Given　the　limitations　of　technology　and　random　noise,　inspection　and　repair　are　always　imperfect.　This　study　considered　imperfect　inspection　and　repair　for　a　system　subject　to　a　three-stage　degradation　process.　The　concepts　of　virtual　age　and　the　improvement　factor　were　adopted　to　characterize　the　imperfect　repair　effect.　To　verify　the　effectiveness　of　the　proposed　model,　we　applied　it　to　the　case　of　a　steel　converter　plant　and　used　the　genetic　algorithm　to　search　for　the　optimal　solution.　The　numerical　results　indicated　that　an　optimal　arrangement　of　inspection　policy　could　significantly　reduce　maintenance　costs.