WCF　Method　is　a　classic　way　to　derive　lower　confidence　limits　of　parameter　functions.　Based　on　the　analytical　expression　of　the　reliability　function　for　general　complex　system　described　by　the　minimal　path,　this　article　gives　the　formula　of　the　lower　confidence　limit　of　reliability　by　WCF　method.　Simulation　studies　for　the　Bridge　system　demonstrate　the　efficiency　of　the　method　and　the　superiority　compared　with　other　methods.　©　2011　IEEE.