This paper analyzed the spectrum character of preponderant vegetables and distilled wave band using the spectrum of the vegetation through field measure in the estuary of Yangtse River. Considering influence factors such as vegetation growth characteristic, season, vegetation cover in tidal shoal，vegetation index of combined characteristic wave bands was used to detect tide shoal's vegetation, in order that it could improve the vegetation classification precision and detect the changes of vegetation environment. The paper computed Vegetation Index of Ratio Vegetation Index（RVI）, Normalized Difference Vegetation Index（NDVI）, SoilAdjusted Vegetation Index(SAVI) and Modified SoilAdjusted Vegetation Index (MSAVI), and analyzed the advantages and disadvantages of the four vegetation indexes in different covers and seasons. Then used these indexes to detect the vegetation classification in TM image. In conclusion, combining the field measure and taking season factor into account for better classification. MSAVI wins the advantage of each vegetation index in classification.