The convetive cloud system on 20 July 2003 in Wuhan region is simulated with a 3-D convective precipitating cloud model. The microphysical characteristics of a mature convective system derived from 3-D cloud model approach to the results from TRMM TMI and PR products. The result from the cloud model is then used as input into a 3-D microwave radiative transfer model that calculates the upwelling radiance received by the rediometer aboard the satellite. The result shows that the structure of cloud has a strong influence on the upwelling microwave radiation.