Using mesoscale numerical prediction model WRF combined with dataset from automatic weather stations, focused on a local convective precipitation process which occurred in and near Tianjin urban area, this paper conducts numerical simulations and sensitivity test to investigate the impact of urban environments (surface features, urban air pollution) on the convective precipitation. The results show that the heat island circulation caused by urban surface changed the position and intensity of convergence line after superimposing sea breeze circulation, which directly affected occurrence and falling area of convective precipitation. Once convection develops, the air pollution over cities can affect the intensity and rainfall. The sensitivity test shows that the increase of aerosol concentration makes the regional average precipitation increased by about 25%. The increase of precipitation is related to the formation of more liquid water in convective clouds.The enhancement effect of aerosol is mainly manifested in enhancing the content of liquid water and ice phase substances in convective clouds.The increased liquid water is transported to a higher level by strong updraft and froze to form ice crystals. The increased latent heat release during this process can also enhance the ascending motion and eventually lead to the increase of total precipitation on the surface. In this experiment, the increase of aerosol concentration can increase the latent heating rate by 110 K·h-1.