Abstract: Based on the results of continuous GPS observation at the fiducial stations and non continuous GPS observation at basic stations in the Crustal Movement Observation Network of China, the annual periodic variations in vertical displacement at fiducial stations are analyzed, and the conditions to obtain long term vertical displacement velocities in China′s mainland from non continuous GPS observations are discussed. It is suggested that the long term linear velocities of vertical displacement at the basic stations (including fiducial stations) from GPS observation of several campaigns are reliable. Because of annual periodic variations of large amplitudes of several cm at some GPS stations and repeated GPS observations of only 2 epochs in 1999 and 2001, the long term vertical displacement velocities at many regional stations are not reliable. The GPS Observations at the basic stations show that the major characteristics of the long term vertical displacement in China's mainland are as follows: the velocities are low in general with uplift in northern part, subsidence in southern part, relatively intense vertical movement in eastern part and weak vertical movement of small subsidence in western part.

Key words: GPS, Basic station, Vertical movement, Tectonic movement