Abstract: Using GPS bending angle and NCEP forecast data , a comparative study was performed to the Beijing rainstorm event on July 21,2012, with and without assimilation of the bending angle data, based on the GSI three-dimensional assimilation system. The result showedthat bending angle data had clear impacts on the temperature and specific humidity fields; the central temperature increment is 0.5 ℃ at500 hPa and -0.6 ℃ at 700 hPa; the central increment of specific humidity at 700 hPa is -0.14 kg·kg-1. Assimilation of bending angle datachanged the stream field and significantly improved the accuracy of the forecast, including the center location of precipitation, rain belt trendand precipitation intensity. According to the threat scores of simulating precipitation, the improvement on the simulation above 200 mm is more evident, but less effective on weak rainfall.