Application　environment　is　the　necessary　condition　for　an　application　system　running.　If　the　application　environment　can　be　trusted,　then　the　application　system　could　run　safely　and　reliably.　This　paper　firstly　analyzes　the　elements　of　application　environment　and　gives　out　the　definition　for　trusted　environment　from　the　perspective　of　process　behavior.　Then　it　discusses　the　decision　theorem　of　trusted　process　based　on　non-interference　theory.　Finally　it　describes　the　design　ideas　of　trusted　application　environment　and　analyzes　its　security.　©2010　IEEE.