Abstract: By GPS positioning, we can obtain the three-dimensional coordinates of stations: latitude B, longitude L and ellipsoidal height H. One of the reason is lower of altimetric accuracy. In order to exploit the potentialities of the accuracy of the heisht provided by GPS position and to make full use of the valuable resources, we analyse the factors affecting the accuracy of the height, propose, the ways and measures to eliminate or reduce the aforementioned errors. Finally an example is given to indicate that the GPS Positioning may be used instead of the first order and second order levelling in determination of crust deformation and other applications.