In this paper,a heavy rainfall occurring in the Yangtze-Huaihe River region during the plum rain season is simulated using the mesoscale numerical model(WRF-V3.4).The Milbrandt-Yau scheme,a two-moment scheme,is chosen,in which the size distribution of each hydrometeor category is described by a Gamma distribution law,and the spectral shape parameter α is fixed.In order to understand the effects of the spectral shape parameters of the raindrops and graupel on the precipitation,the precipitation,water content and concentration distribution of the hydrometeors,as well as the source and sink terms of the raindrops and graupel,are analyzed through several sensitivity experiments with different values of raindrops and graupel,and different spectral shape parameters.The results show that the distribution of raindrops and graupel is greatly affected by the spectral shape parameters thereof,as it can affect the micro-physical processes associated with rainwater and graupel.When the spectral shape parameters of the raindrops increase,the raindrop evaporation first increases then decreases,while the collision of the graupel and clouds also decreases.At the same time,when the spectral shape parameter of the graupel increases,the graupel melting decreases.Therefore,the change of the two parameters leads to differences in precipitation distribution and magnitude.