Wuhan Technical University Surveying and Mapping (WTUSM) carried out three GPS campaigns in the Tibetan Plateau since 1993. To improve the vertical component precision of GPS measurement, we estimated the remaining tropospheric refraction using the piecewise linear method after the SAASTAMOINEN model and corrected the tropospheric refraction by selecting one parameter for every two hours model to consider the variation of tropospheric refraction. Using the IGS combined ephemeris and corresponding EOP Series for 1995 and 1997 GPS campaigns, all baseline vectors were processed by GAMIT (Ver.9.71) software, and network adjustment was carried out in ITRF97 frame by PowerAdj software (Ver.3.3) which was developed by WTUSM considering the baseline vectors'full covariance matrix. The resulting vertical velocity field determined from GPS campaigns in 1995 and 1997 shows that the average uplift rate in ITRF 97 frame is about 7.8