The difference of the water extraction methods by using of the five different index models(i.e.RVI,NDVI,NDWI,MNDWI and NDSI) is studied through the analysis of the specific theory and the specific examples(Dongting lake areas) .So that help to choose the proper model which is determined for water extraction should be available in different time and for different purpose.The purpose of monitoring the eutrophication of Dongting lake areas is taken,so the MNDWI model was selected for water body extraction.