After　defining　two　ideas　lattice　and　convert　channel,　this　paper　analyses　detecting　methods　of　convert　channel　including　SRM,　syntactic　information　flow　analysis,　semantic　information　flow　approach　and　non-　interference　method.　This　paper　put　forwards　one　method　of　improved　syntactic　information　flow　processing.The　idea　in　this　kind　of　method　is　that　we　design　PC　to　sign　every　row　of　program,　and　detect　the　covert　information　flow　by　this　kind　of　data　structure-stack.　©　2010　IEEE.