By statisically analyzing many MODIS images, an empirical algorithm is described, which is used to determine the case II water from the MODIS image. The algorithm takes advantage of the characteristic that the apparent reflectances of the case I and case II waters are the same in SWIR band, but considerably different in the visible band. The empirical algorithm was applied to MODIS images over Bohai, China, the waters in Bohai were classified into two types: case I and case II. The results show that the proposed classification empirical algorithm is precise and effective.