Probability　analysis　on　the　durability　life　of　concrete　structure　under　the　chloride　environment　is　little　known.　Using　the　probability　method　on　the　basis　of　the　second　Fick＇s　law,　research　work　was　carried　out　to　investigate　the　distribution　factors　that　may　influence　the　durability　life　of　concrete　structures.　Due　to　the　deficiency　of　the　decisive　method　for　prediction　of　durability　life,　a　method-based　on　the　regulated　reliability　index　is　proposed.　The　relationship　between　the　durable　reliability　index　and　the　corrosion　time　is　established.　The　present　paper　takes　the　time　when　the　durable　reliability　index　falls　below　a　stipulated　index　as　the　end　of　durable　life.　The　proposed　predictive　method　of　durability　life　for　concrete　structure　under　the　chloride　erosion　environment　is　therefore　improved.