The explosive growth of algae in inland water bodies is one of the major water environmental problems in China, and it’s very important to monitor the dynamic of algae in both temporal and spatial scales. In the present paper, a model, which was used to extract the algae information from the water body of Taihu Lake using MODIS data, was established based on the remote sensing index and image false color composite methods. Using this model, we studied the algae explosive growth formation process between March and May in 2007. Through the analysis of the temporal and spatial distribution features of the algae outbreak between the spring and summer seasons, an early warning method of algal blooms was proposed, that is, when the MODIS green index mainly concentrated in the range between 0.6 and 0.8, the water body of Taihu Lake can be considered to have been in the early alarming stage of algal blooms.