Abstract: A microwave canopy scattering model was developed for estimating rice biomass effectively. Taking paddy rice biophysical parameters measured in field survey as inputs of modified microwave canopy scattering model to simulate backscattering coefficient of paddy rice canopy, the modified model was integrated with generic algorithm optimization tool (GAOT) for the inversion of rice biophysical parameters from radar data ALOS/PALSAR. And then, a rice biomass map was generated. The results showed that the estimation error of rice canopy backscattering coefficients was less than 1dB with the modified model, and the difference of rice biomass between measured and estimated was below 200 g/m2. This research showed the potentials of microwave remote sensing physical model for inversing rice biophysical parameters and estimating rice biomass.