Abstract: Before the 9th July 1979 Liyang earthquake,beginning from mid June the vertical component at the Liyang station about 20km from the epicentral area decreased gradually to a negative anomaly. After decreasing to the lowest level in the last ten days of June,it increased quickly to a positive anomaly. Just before the tectonic event,the observational value was brought back to its initial value. It is consigderd that the seismic fault perhaps responsible for the shock trends WNW or NNE. The shear stress piezomagnetic modol by Stacey has been used to calculate the theoretical values of the surface Z-component anomaly for this skock.A comparision of observations with the theoretical values shows that there have bsen the strong tectonic activities along both the faults. The shock was probably accompanied by conjugated offset on the faults.