In consideration of the spectral character of MODIS (Moderate Resolution Imaging Spectroradiometer) data and the reflective spectrum of vegetation and soil, NDVI (Normalized Difference Vegetation Index) and NDWI (Normalized Difference Water Index) are deduced using one visible band (0.66μm) and two near-infrared bands (0.86μm, 1.24 μm). Vegetation canopy temperature is derived using two thermal infrared bands (8.6 μm and 11μm). Then the vegetation/soil synthesis water index (VSWI) is acquired through analyzing the coupling character of three indexes which can reflect the water condition of vegetation. Finally, the synthesis index is verified by equivalent water content of a single leaf. The matching results show that the synthesis index is directly proportional to the modeled data, which means that the vegetation water content can be reflected using the synthesis index effectively.