The Beidou Groundbased Augment System is the important infrastructure of the Beidou Satellite Navigation System. To obtain water vapor products with high precision and resolution is the demand for numerical forecasting, space weather monitoring and early warning services. This paper, using the data from three kinds of water vapor patterns of Beidou, GPS and GPS + BD in Beidou Groundbased Augment System, combined with the radiosonde observation, makes detailed comparative analysis among Beidou, GPS and sounding systems. The results show that: (1) The data provided by the Beidou Groundbased Augment System can be effectively used to retrieve the total vapor content of the atmospheric column, and the average deviation is less than 1 mm, which is basically consistent with the GPS and the sounding system and has some indication to numerical forecast. (2) Compared with the GPS system, the mean square error of GPS/PWV and GPS+BD/PWV is less than 2 mm, and the correlation coefficient is more than 97%, which indicates that the accuracy is similar to GPS system. However, the mean square error of Beidou/PWV is 3-6 mm, and the relative variance is 15%-20%, which shows that there is a certain difference of accuracy between Beidou and GPS system. (3) Compared with sounding system, the Beidou/PWV has some inconsistency with the situation in individual time changes, which the mean square error is 2.14-6.12 mm and the relative variance is 15.32%-20.84%. The errors may be due to factors such as the detection system errors, while the GPS+BD/PWV and GPS/PWV will be more stable.