In　order　to　improve　the　results　quality　of　storm　water　detention　storage　design,　the　paper　puts　forward　a　feasible　design　method　to　calculate　the　stormwater　detention＇s　storage　by　using　finite　difference　method,　researches　the　calculation　process,　and　models　the　drainage　system　to　check　the　calculation　result.　The　research　result　demonstrates　that　this　method　takes　effective　measures　to　calculate　the　detention　storage　and　also　is　very　helpful　for　practical　design.