This paper discusses the method and mechanism of identifying and monitoring the cyanobacteria bloom based on MODISdata in Lake Taihu. Through the comparison of spectral reflectance value of different cyanobacteria concentration, it can be foundthat several wave bands are sensitive to cyanobacteria. Making use of the color composition, we can get the macroscopic distributioninformation of the cyanobacteria bloom. Furthermore, using the ratio index model, we can further confine the relative content of thecyanobacteria bloom. Finally through overlaying analysis of the cyanobacteria concentration distribution from multi-temporalMODIS data, dynamic changing information of cyanobacteria bloom can be obtained.