Abstract: The Tangshan earthquake is called the successive earthquake because the strong earth-quakes accurrcd continuously.The paper studies the cause of the successive earthquake from tbe three aspects as follows: tectonics, earthquake preparation and mechanics.It is suggested that successive strong earthquake activity in Tangshan seismic region is on the base of its particular concditions of structure and earthquake preparation;and of that stress field in North China seismic region,specially in its Northeastern subarea,is obviously increassed.In addition, both dip angle of conjugate faults and Tangshan fault zone played an important role.