Abstract: Water vapor is an important parameter for weather forecast weather, so it is important to obtain high resolution water vapor products in time. Aiming at the slow update speed and long delay of final precise ephemeris, which can't meet the requirement of real-time retrieving atmospheric precipitable water, a method of retrieving atmospheric precipitable water by using ultra-fast ephemeris instead of final precise ephemeris is proposed. Based on the principle of ground-based GNSS inversion of atmospheric precipitable water, using GAMIT software, the atmospheric precipitable water is obtained according to the ephemeris products with different precision provided by the international GNSS service (IGS) website, and compared with the atmospheric precipitable water obtained by meteorological sounding station. The results show that the atmospheric water obtained from the super fast ephemeris can be consistent with the final precise ephemeris. The average difference is smaller than 0.1 mm, and is consistent with the atmospheric precipitable water measured by the sounding station. The accuracy of the two ephemeris can meet the needs of weather forecasting.