A heavy precipitation process in east China during July 23-24, 2009 is simulated to conduct a sensitivity experiment by WDM6 and Morrison schemes in WRF model. The accumulation precipitation, rain intensity and the microphysical cloud-parameters are analyzed in two simulations to assess the two microphysics schemes in precipitation prediction. Compared to the observation of the heavy rainfall, the underprediction of precipitation and the earlier rain starting are simulated by WRF model with both cloud microphysics schemes. However, the precipitation prediction with the Morrison scheme is more reasonable, while the WDM6 scheme produced a higher error above 50% compared to the observation. Due to the unreasonable definition of raindrop of WDM6 scheme, more raindrops whose size are smaller than the reasonable raindrop size distribution were modeled. Based on a calculation, it is found that the unreasonable definition of raindrops in WDM6 scheme might lead to an overestimation of evaporation and an underestimation of sedimentation for the raindrops, resulting in the underprediction of accumulated precipitation on the ground.