Probability　distribution　law　of　corrosion　initiation　time　of　steel　in　concrete　under　chloride　environment　is　discussed.　Based　on　the　Fick＇s　second　law,　by　Monte　Carlo,　frequency　distribution,　distribution　type　and　probability　density　is　analyzed.　The　statistic　parameters　of　the　factors　influencing　the　probability　distribution　of　corrosion　initiation　time　are　studied　and　the　expression　for　sensitivity　analysis　of　corrosion　initiation　time　is　deduced.　By　sensitivity　analysis　can　know,　corrosion　initiation　time　is　found　to　be　more　sensitive　to　cover　than　the　diffusion　coefficient,　and　more　sensitive　to　surface　chloride　concentration　than　the　critical　chloride　level.　The　analysis　of　the　paper　perfects　the　methods　of　predicting　the　corrosion　initiation　time.　©　(2011)　Trans　Tech　Publications.