Because cloud plays an important role in earth climate change, cloud monitoring is an important part in the research on global climate change. At present, the meteorological experts and amateurs pay more attention to the research on cloud monitoring. Therefore, cloud detection has become a topical issue at present. The data from the Japanese meteorological satellite GMS-5 are used for cloud detection research. Firstly, the infrared bright temperature method is used for coarse detection of cloud. Then, the methods of similar degree of consistency, space detection and visible light reflectivity are used to detect in clear sky. The final results show that the combination of these three methods in cloud detection can judge whether it is the clear sky radiation or the radiation from cloud well.