The　probabilistic　model　of　corrosion　initiation　time　of　steel　bar　in　concrete　structure　in　chloride　environment　is　established　on　the　basis　of　the　Fick＇s　second　law.　By　means　of　Monte　Carlo　method　the　frequency　distribution,　distribution　mode　and　probability　density　function　are　investigated.　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.　The　sensitivity　analysis　result　shows　that　the　initiation　time　is　more　sensitive　to　the　critical　chloride　level　than　the　surface　chloride　concentration.