Using rapid radiative transfer model CRTM, the sensitivity of microwave surface emissivity microwave brightness temperature (TB) to landsurface and cloud parameters is analyzed. First, the accurate measured ground and sounding data of Yunnan Simao are used as input of CRTM to simulate 12 microwave channels’ surface emissivity and TB, then the simulated TB is compared with AMSR E satellite TB data, and, moreover, the simulation error and sensitivity to each parameter are analyzed. The results show that soil moisture, surface temperature and vegetation fraction have a great influence on TB simulation, and simulated surface emissivity is affected by soil moisture and vegetation fraction. The influence of precipitation clouds is bigger than non precipitation clouds. Among the 6 kinds of clouds, the rain cloud has the biggest influence. In the clear sky condition, most of the 12 channels’ simulation errors are between 0 to 3 Kelven. Channel 10.65 V is hardly affected by cloud and rain, but it is very sensitive to the landsurface parameters.