Abstract: In this paper, we present an evaluation of the water vapor tomography results from four systems-GPS, BDS, GLONASS, and Galileo in terms of accuracy, using the proposed water vapor tomography profile evaluation index TPFS. The results show that the differences in the water vapor tomography solving results of each GNSS are negligible, with the maximum RMSE difference being within 11%. Among these, BDS performs the best in water vapor tomography, while GLONASS performs the worst. Compared with GPS, GLONASS, and Galileo, BDS has a significant advantage in the lower layer (below 2406m). In particular, in the bottom layer, BDS shows a respective improvement of 3.2%, 16.2%, and 5.2% in RMSE compared to GPS, GLONASS, and Galileo. Furthermore, in the comparison of TPFS of tomography water vapor profiles, BDS has the smallest average TPFS and the lowest TPFS of water vapor profiles under heavy rainfall, which is improved by 25.2%, 31.5%, and 32.8% compared to GPS, GLONASS, and Galileo.