Based　on　the　analysis　of　chloride　ion-induced　erosion　mechanism　of　reinforced　concrete　and　the　Fick＇s　second　law,　a　multi-factor　model　of　the　chloride　ion　erosion　is　established.　In　this　model,　the　influences　of　water-cement　ratio,　humidity,　time,　temperature,　and　chloride　ion　binding　capacity　of　concrete　are　taken　into　consideration,　and　the　mathematic　solution　to　the　new　model　is　provided　by　considering　the　boundary　conditions.　The　new　model　is　verified　by　analyzing　the　long-term　exposed　experiment　data.　Compared　with　the　traditional　model　of　Fick＇s　second　law,　the　model　can　indicate　the　development　trend　of　the　structure　eroded　by　chloride　and　the　chloride　ion　concentration　in　different　depth,　and　at　the　same　time,　it　can　predicate　the　chlorine　ion　concentration　on　rebar　surface　in　different　corrosion　periods　and　the　initiation　corrosion　time　of　reinforcement.