To　solve　the　problems　derived　from　isolation　of　application　security　mechanism　and　operation　system　security　mechanism,　firstly,　the　concept　of　security　channel　and　TCB　extension　was　proposed,　and　then　formal　description　of　security　channel　was　given.　By　practices,　a　TCB　extension　model　which　based　on　security　channel　was　obtained.　This　model　could　be　used　to　explain　how　to　build　security　channel　between　different　security　mechanisms　in　order　to　achieve　uniform　and　eliminate　conflicts　of　those　security　mechanisms.　Finally　the　theory　and　practicality　of　this　model　with　security　analysis　and　engineering　implementation　were　proven.