Abstract: The ability of TRMM/TMI for flooding and soil wetness detection has been demonstrated in this st udy. On the basis of TMI measurements, four methods, the classification method, the soil wet ness index (SWI) method, the polarization difference index (PDI) method, and the polarization ratio index (PRI) method, were brought out to monitor flooding and study soil wetness in the Yangtze River and the Huaihe River basins during the summer 1998. Compared the images provided by L-band Synthetic Aperture Radar (L-SAR) and Radar Satellite (Radarsat) with the figures derived from daily rainfall data based on the Zindex method, the flooding and soil wetness detection by TMI was proved to be feasible.