In　a　multi-state　system　with　common　bus　performance　sharing,　the　residual　performance　of　any　sub-unit　can　be　shared　to　other　sub-units　with　insufficient　performance　by　the　common　bus　with　stochastic　sharing　capacity.　This　study　extends　the　reliability　evaluation　model　by　considering　both　the　minimum　and　maximum　requirements　of　elements,　which　should　not　only　meet　the　random　minimum　requirements　of　each　single　element,　but　also　require　that　there　should　be　no　excess　performance.　The　reliability　of　the　multi-state　system　(MSS)　is　estimated　by　using　the　Universal　Generating　Function　(UGF)　technique.　Illustrative　example　is　presented　to　illustrate　the　procedures.　In　addition,　the　genetic　operator　is　used　to　obtain　the　optimal　location　of　the　components　with　maximum　reliability.