Abstract：Based on previous studies, the rupture parameters of the 1970 Tonghai MS7.7 earthquake are obtained. Using the model, we study the changes of Coulomb rupture stress under different lithospheric rheological properties. We discuss the effects of static co-seismic deformation and short-term post-earthquake deformation on potential seismic activity in the Xiaojiang fault and the Red River fault. Results show that on some segments of the two faults, the coseismic change of Coulomb failure stress(ΔCFS) attains 0.12-0.50 bar at 7.5 km depth. Relaxation of the lower crust and the upper mantle adds the postseismic ΔCFS on the two faults up to 0.22-0.90 bar after 48 years. This means that the 1970 event is increasing the potential of seismic activity along the two active faults. In this case, we should pay more attention to these two active faults in future research by increasing field observations to monitor the seismic activity and the crustal motion pattern.