Abstract: This paper, using the geomagnetic absolute observation data F and Z from Changli, Qingguang and Hongshanstations, computed the slope of regression straight line of these two quantities in a plane right angle coordinate, and the mid-error and correlation coefficient of each quantity of Changli station. The result shows that the slope of Changli station which is the nearest station to the epicenter showed an obvious anomaly before the Tangshan earthquake, which lasted to the occurrence of the earthquake and turned to its normal in August. At the same time, Qingguang station which is further away from the epicenter also ahowed an anomaly, but its amplitude is smaller than that of Changli station, it showed an obvious anomaly before the Ninghe M6.9 earthquake on Novemberm 15th near the station. The slope o f Hongshan station which is far away from the epicenter showed little changes. By analyses, it is considered that the geomagnetic anomaly of Changli station before the earthquake belonged to regional anomaly, which might be caused by this strong earthquake; meanwhile the anomalies before the earthquake contracted from the focal volume margin to the epicenter.