An improved method for detecting cloud combining Kmeans clustering and the multi-spectral threshold approach is described.On the basis of landmark spectrum analysis, MODIS data is categorized into two major types initially by Kmeans method.The first class includes clouds, smoke and snow, and the second class includes vegetation, water and land.Then a multi-spectral threshold detection is applied to eliminate interference such as smoke and snow for the first class.The method is tested with MODIS data at different time under different underlying surface conditions.By visual method to test the performance of the algorithm, it was found that the algorithm can effectively detect smaller area of cloud pixels and exclude the interference of underlying surface, which provides a good foundation for the next fire detection approach.