In　order　to　verify　the　trustworthy　of　component-based　system,　B　method　is　applied　to　define　the　specification　of　component　interfaces　and　verify　trustworthiness　of　component　connections.　A　case　study-steam　boiler　concerning　a　real-time　system　is　analyzed　and　its　component　model　is　given.　Furthermore,　the　trustworthy　constraint　is　added.　By　virtual　of　Atelier　B　tool,　the　model＇s　correctness　is　verified.