The annual gravity variation in the same measuring position, which is for seismic monitoring by repeated measurement, is about more than a few tens 1 × 10-Sm · s-2 However, since the topography of the measuring position is varying from point to point, the gravity anomaly gained through gridding will be influenced directly. So we calculated the topographic effects with different scales and depth of field sources by the hexahedral model in this paper, and with this as the basis, we analyzed the gravity observation data of the eastern margin of Qinghai-Tibetan plateau, and removed the influence of the terrain by the method of potential field continuation. The results showed that this method was efficient in improving the quality of the gravity data, which was more helpful in cognizing the space characteristics of gravity anomaly and also the gravity field variation by repeated measurements.