To extract information about the Earth's surface from Earth Observation data, a key processing step is the separation of pixels representing clear-sky observations of land surface from observation influenced by cloud. This paper presents a new method used for MDOIS data over Tibetan plateau and desert. The method for cloud detecting based on the difference on band 6 (apparent reflectance of blue band) and band 31 (bright temperature in thermal infrared band) between cloud and land surface. Experimental results show that the method is feasible.