On the basis of the MODIS remote sensing images, the bluealga bloom over the Dianchi Lake was monitored by the pseudocolor composition (RGB: 621) and the normalized vegetation index methods, according to the spectral features in the blue, red, and nearinfrared wavebands. Through the satelliteground synchronization experiments, the accuracies of the two methods are verified. The pseudocolor composition method uses color difference to display bluealga bloom, which has better visual effect, while the normalization vegetation index method uses index values to decide bluealga bloom concentration quantitatively, which can be applied to quantitative investigation.