To apply multichannel remote sensing technology to cloud remote sensing based on groundbased infrared sensors，the SBDART model is used to calculate the atmospheric downward infrared radiation of double bands（103 to 113 μm，115 to 125 μm），from which the characteristics of the brightness temperature difference are analyzed and the influences of the different visibilities and sky statuses on brightness temperature difference are discussed.The simulation results are compared with that in the real sky status. It is shown that in the perfect visibility situation，the change of the radiance at the zenith is more evident than that at the horizon，and the different characteristics of the brightness temperature difference in the different sky statuses can be adopted to identify clouds under higher visibility within a certain range of zenith angle.