Abstract: Based on the seismological observations, this paper presents some characteristies of seismicity variation before 4 Tangshan trong after shocks.Tbe result shows that the freq-uency of Tangshan earthquake sequence, seismic wave energy,b-value and epicentrl distrib-ution pattern abviously changed before the strong after shocks.After discussion, it has been considered that these variations were caused by elosed section formed by strong after shock a ults, tbey were related with atrong after shock preparation, and so they can be used as precusory information.