Operational bloom remote sensing monitoring usually uses MODIS data with 250 meter resolution. However, most of the remote sensing image pixels are mixture of water and algae bloom. Using images with 250 meters resolution to extract algae bloom area will seriously affect the accuracy of algal bloom monitoring. Aimed at solving this problem and based on the mixed pixel model, the authors used the decomposition of mixed pixels to extract bloom component abundance in the mixed pixels. Compared with the traditional methods, the approach proposed in this paper improves the extraction accuracy of algae bloom area by nearly 30 percent; in addition, this approach is capable of reaching the algae bloom area extraction at the sub-pixel level, thus improving the accuracy of remote sensing. In practical application,this approach can extract algae bloom area by using DN values of remote sensing image without the pre-processing of radiation and atmospheric correction for remote sensing image.