Abstract: Since microwave signals are very sensitive to the variability in the type and structure of precipitation clouds, retrieving the precipitation cloud parameters based on the satellite borne microwave observations is still one of the most challengeable problems. In order to investigate the characteristics of microwave signals on TMI channels in responding to two precipitation cloud types of stratus and convective clouds, a radiative transfer model (MWRT) with a better treatment of the solid precipition particles is used in this paper to simulate microwave brightness temperatures (TB) under the condition of different surface and precipitation cloud parameters. In addition, variations of combined TB from multiple channels are also analyzed which include the polarization difference ( D ) as a mirror of emission signals (for ocean) as well as the 85 GHz polarization corrected temperature (PCT85) for ocean and the vertical frequency polarization difference (VFD) for land as functions of scattering signals, so as to theoretically explore the precipitation retrieval method. The results show that both of D and PCT85 decrease as increasing rain rate over ocean, among which D 10 and PCT85 are able to reflect well the variation of rain rate but with the former in a greater extent affected by the surface conditions and the latter by the cloud properties such as the height of the freezing level and the size of graupel. On the other hand, though D 19 and D 37 are insensitive to both surface conditions and the height of the freezing level they show no polarization difference in the case of high rain rate, implying that they are unsuitalbe to vetrieving rain rate. Over land, the VFD with the higher frequency as 85 GHz shows a good response to rain rate and augments with increasing rain rate, among which VFD37 85 is hardly influenced by surface conditions but strongly affected by cloud properties. Especially, for the channel of 37 GHz, owing its high sensitivity to variations in liquid water so that scattering signal is easily confused by emission signal, it is difficult that the VFDs with the higher frequency like 37GHz are applied to investigate the relationship between rain rate and microwave signals. Besides, since the existence of graupel in convection clouds would have complicated the characteristics of scattering signals, PCT85 and VFD would worse respond to rain rate for convection clouds than for stratus clouds. Based on the results above, a theoretical approach to retrieving rain rate can be suggested as follow: over ocean it is preferred to use D 10 with proper surface conditions or PCT85 with proper height of freezing level, and over land use VFD3785 with proper type (stratus or convection) of precipitation clouds.