Abstract: In order to resolve the normal. height of GPS nets in mountainous area, a new geometric method considering terrain effect is discussed in this paper. The mathematical model of the new method is also given. Besides, the accuracy of this method using non-grid height's data is also analyzed. The effect of using non-grid data and interpolation method on calculating normal height is estimated. In order to improve interpolation accuracy in the area where terrain changes very greatly, topographic map of GPS net is advised to use for practical application. Of course, net shape and number of GPS leveling points should also be considered in practical calculation. If the condition can't meet in practical wok, the correspond measurements are given in the paper. Using the new method,a few of GPS nets in mountainous area have been tested in the paper. The result shows that the accuracy of this method in mountainous area approximates as high as in smooth area. All these show that height determination with GPS leveling data considering non-grid data and effect of terrain valid in mountainous area.