Using the GPS analysis software GAMIT and combined with the surface temperatures and pressures,the precipitable water vapor(W_P) at a timal resolution of two hours has been retrieved from the GPS observations in Beijing from July 2004 to July 2005.Compared with the records of the radiometer and the water vapor radiometer,the results show a good agreement with the rms 3.05 mm and 3.29 mm respectively.Further,the seasonal variation of W_P and the relationship between W_P and rainfall in Beijing are also discussed in this paper,which are beneficial to the weather study and weather forecast.