Abstract: the earthquake activity is mainly medium events in Capital zone in recent years.The characteristic of seismicity anomalies before medium earthquakes is studied with the parameters that reflect frequency, energy, mean magnitude, such as frequency, earthquake deficiency, total area of fault plane and degree of seismicity.It is found that most of the anomalies have good correspondence with the medium events in Capital Zone from 1999 to 2001, and the accuracy is high when 3 low value anomalies appear.This method is effective in the prediction in Capital Zone, such as the prediction of Luanxian M4.2 earthquake occurred on Dec.28, 2001.Since the effect of parameters' index that reflects earthquakes has some phasic change and regionality, we need adjust the indexes continuously to capture more seimic information.