Abstract: In order to investigate land resources and prevent flood and disaster, a GPS geotectonic deformation-monitoring network was established to monitor the tectonic subsidence of the flooded area in the middle reaches of the Changjiang River. Considering the affect of tropospheric delay, the mete orologic data at every site were surveyed. The Saastamoinen model was adopted t o compute the dry component parts of the tropospheric delay in the data processing of GPS monitoring network. The wet components of the tropospheric delay were estimated by using the piece wise linear method for improving the precision of G PS height components. The repeatability of all baselines of GPS monitoring netwo rk was superior to 10-8 level. The horizontal RMS(root mean square) errors of all monitoring points were superior to ±2.6 mm and the height RMS error s of all monitoring points superior to ±3.3 mm. The relative accuracies of all baselines after adjustment were superior to 10-8 level. The research indicates the accuracy of the GPS monitoring network can be achieved and satisfy completely the accuracy requirement of the geotectonic deformation monitoring.It can offer the exact vertical deformation information for the geological inves tigation and preventing disaster.