In terms of analysis on the continuous change curves of radon in groundwater at more than twenty measuring points along the north China and North-South tectonic belt,it is found that the tendenciously high value anomaly and abrupt anomaly were common during the high seismicity period from 1966 to 1976.But during the low seismicity period from 1977 to 1985,the groundwater radon value is stable except the short-term tendency anomaly or abrupt anomaly at few points in local area,It is considered that the hydrochemical anomaly field under the action of the regional stress field during high seismicity period is an important indication for the prediction of one-by-one strong events.