By using of an hourly precipitation of 162 heavy rain days at 11 stations of sanming city,Fujian province in May and June from 1980 to 1998,the spatial and temporal distribution,moving features,precipitation process and influential system of rain cluster and severe rain cluster in heavy rain days of flood season,as well as topographic effect were analysed.Some features and active regularity of the medium scale precipitation in sanming city were described.