The combined atmospheric radiative transfer model based on MODIS level2 cloud products and atmospheric products was used to simulate brightness temperature at the top of atmosphere with water clouds at 8.55 μm, 11.03 μm and 12.02 μm bands. The brightness temperatures between model and MODIS observation at 8.55 μm,11.03 μm and 12.02 μm bands were compared and analyzed . Results show that brightness temperature simulated by Combined Atmospheric Radiative Transfer model based on satellite cloud parameters, atmosphere parameters and space geometric parameters is basically consistent with MODIS observation. The brightness temperature difference between them is quite small. And brightness temperature difference between model and MODIS is mostly at the range of －10 K~10 K. Varieties of brightness temperature BTD(8.55~11.03 μm) and BTD(11.03~12.02 μm) of model were accordant with conditions under water clouds.