Xiashan　Reservoir　is　a　large　reservoir　lies　in　Weifang　City,　Shandong　Province.　With　the　development　of　economy　and　society,　the　deficit　in　water　resource　has　increasingly　arisen　in　many　cities,　such　as　Weifang　City.　Considering　thoroughly　the　uncertainties　of　flood,　wind,　storage　volume　and　discharge　capacity,　the　overtopping　risk　analysis　for　earth　or　rockfill　dam　against　the　simultaneous　actions　of　flood　and　wind　wave　during　flood　period　has　been　established　in　the　paper　and　then　its　application　to　Xiashan　Reservoir　is　described.　By　taking　10-6　as　acceptable　risk,　or　99.999%　as　acceptable　reliability,　the　result　of　risk　analysis　show　that　the　earth　dam　of　Xiashan　Reservoir　is　very　reliable　against　the　design　series　of　flood　events　accompanied　with　the　runup　generated　by　wind　wave　during　flood　period.　Besides,　in　order　to　efficiently　utilize　the　valuable　water　resources　(including　flood　period)　upstream　of　the　reservoir,　on　the　basis　of　risk　analysis,　we　recommended　that　its　designed　limiting　reservoir　level　before　flood,　say　37.4　m,　may　be　safely　raised　to　an　new　elevation　of　38.0　m.　The　correspondent　increment　of　water　volume　should　be　7765　×　104　m3.　It　would　bring　a　great　deal　of　direct　benefits　and　social　benefits.　©　2014　Taylor　&　Francis　Group.