Based on the Mesoscale Eta coordinate Model (MEM), which contains 16 levels in the vertical with different intervals, a high resolution PBL scheme with 21 levels is introducted. Using the improved model, the numerical simulations of heavy rain case are done. The results show that the improved model has a great progress in the heavy rain forecast, the TS score for the precipitation, especially, for the heavy rain, is obviously higher than the former model. This is very important in the model′s operational use in the near future. The sensitivity test shows that it is useful for the heavy rain forecast with increasing the model′s vertical resolution. Additionally, the model is sensitive with the mixing length and the moist available quotiety, and influence of the features of model underlying on the prediction results is important.