With the software of GAMIT 10.6 and the GPS observation data at Nanchang Station, a set of 13 tests about the influence of approximate coordinate on the solving of GPS PWV are carried out. The results show that when the distance between the approximate coordinate and actual coordinate is less than 60 m, the approximate coordinate has weak effect on GPS PWV. But when the distance exceeds 60 m, the variation of approximate coordinate significantly affects the solving of GPS PWV. The relative error of baseline and the standard deviation between GPS PWV and sounding PWV increase rapidly, while the days of successful solving GPS PWV decrease rapidly with the increasing of the distance (when the distance ≥120 m, the day is 0). Meanwhile, NRMS (normalized root mean square) and the correlation between GPS PWV and sounding PWV also has a significant decrease when the distance is more than 60 m. Additionally, the effects of variation of approximate coordinate on the relative error of baseline, NRMS, and the accuracy of GPS PWV only occur at local station.