The Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) is very sensitive to hydrometeor, including liquid and solid water in various forms such as rain, ice, snow, and graupel. The purpose of this paper is to analyze the influence of hydrometeor on TMI channels by using Weather Research and Forecasting model (WRF) output to reconstruct the atmospheric state, cloud information and simulated brightness temperature (TB) from Radiative Transfer Model (RTM) calculation. The result shows that the rain may affect on 19 GHz TB of TMI, while the graupel has the most important factor influencing on 85 GHz. The ice and snow does not show a significant effect on any channel of TMI. Because the graupel is typically found in the strong convective clouds, such clouds will lead to heavy rainfalls rate. Therefore, 85 GHz channel is suggested for estimating heavy rainfall rate.