A new assimilation module of AMSR2 (Advanced Microwave Scanning Radiometer 2) radiance data was constructed in WRFDA-3DVAR (Weather Research and Forecasting model's 3-dimensional variational data assimilation). With this module, the impact of AMSR2 assimilation on the analysis and forecast of Typhoon Son-Tinh was evaluated. AMSR2 data is able to detect Son-Tinh's cloud band pattern. Compared to the experiment without AMSR2 assimilation, AMSR2 assimilation provided a better typhoon structure, and significantly improved the central sea level pressure, maximum wind speed and typhoon track forecasts.