Abstract: The Temporal sequence curves and spatial isolines of gravity variation are drawn, and the dynamic variation and its characteristics of gravity anomalies before Zhangbei 6.2 and Datong 5.6 earthquales in 1999 are analyzed.The results show, the process of seismogeny is relative to the variation of gravity field;earthquakes usually occur in the descending period of gravity;the epicenters are usually located at high grads region.