Jiuxi basin, a compressional basin in western segment of Hexi Corridor, had developed several late Quaternary reverse faults and fold zones, and is a potential seismic source of strong earthquake in future. In this paper, taking Yumen potential seismic source zone as an example, the long-term seismic activity levels of 9 potential seismic sources near Jiuxi basin are compared. It is found that seismic activities of seismic sources in same magnitude grades are nearly in the same level respectively. Basing on the result, it is feasible that determination of the upper-bound magnitude of Yumen potential source is Ms7. 0. So, comparing seismic activities level in long term is a auxiliary measure for determination of potential seismic source zone.