In large scale gravity prospecting, when total accuracy of Bouguer gravity anomaly is increased to 0.025×10^-5m/s², the height mean square error of the measuring point must be 0.050 m. Using EGM2008 model and GPS leveling data to fit local quasi-geodic surface, the authors transformed the altitude of the measuring point GPS, thus reaching the accuracy. By using GPS leveling data of a certain area, the authors studied the feasibility of the transforming method. The result shows that the method is completely applicable to large scale gravity prospecting.