Abstract: We introduce a structure of the GPS real-time dynamic geometric deformation monitoring system and the instrumentation deployment.Accuracy of the monitoring system is estimated based on the data collect during Sutong Bridge construction.The results indicate that the accuracy is better than 5-10 mm in horizontal and vertical directions,respectively.Displacement responses of the tower caused by thermal loading effects are analyzed and some advice is given.Spectral analysis is used to compute the modal frequency of the bridge pylon tower and the cantilevers using GPS monitoring data.Dominant frequencies derived from GPS monitoring data and the finite element model are compared and the results indicate that identification of modal parameters using GPS data is reliable.