Rainfall　is　the　main　driving　force　resulting　in　soil　and　water　loss.　Commonly,　it　is　quantitatively　assessed　by　rainfall　erosivity　index　(REI)　which　is　denoted　as　R.　The　classical　method　for　calculating　the　value　of　R　is　precise,　but　is　very　complicated,　and　the　required　data　is　difficult　to　obtain.　So　how　to　ensure　the　model＇　s　precision　while　reduce　its　complexity　is　the　key　to　establishing　a　simple　and　easy　method.　Based　on　several　rainfall　observed　stations＇　data　of　recent　years　in　Changting　County,　this　paper　creatively　used　the　method　of　multiple　regression　analysis　and　proposed　a　new　simple　and　easy　algorithm　of　REI　for　Changting　County　with　reference　to　the　results　of　classical　method.　With　the　proposed　method,　REI　of　the　mentioned　area　was　calculated.　Then　the　spatiotemporal　distribution　of　R　in　the　county　and　its　relationship　with　soil　erosion　were　analyzed.　It　turns　out　that,　the　accuracy　of　the　method　presented　herein　is　much　better　than　that　of　similar　research　for　the　same　region,　and　that　the　analysis　conclusions　agree　with　the　actual　situation.