Abstract: In this paper, some characteristics of the Tangshan earthquakes were discussed from the data of focal mechanisms. The fault plane of the main shock is a bilateral strike-slip fracture along N30℃ and appears clearly to control the aftershocks so that the stronger aftershocks occurred concentratedly around the two stopping positions of the fault plane. This was determined by the distribution of remaining stress over the fault plane of main shock after its occurrence. The larger differences of the fault plane solution of some aftershocks and the higher percentages of the inconsistent first motions in the composite fault plane solutions of aftershocks imply that the fractures and the redistribution of the stress in focal region after the occurrence of main shock were complicated. The decrease of the percentage of inconsistent first motions in the later composite fault plane solution shows probably an indication that the medium in the focal region was going from a strained equilibrium, to a lax equilibrium. It was pointed out from the analysis of seismic data that the fault plane solution of main shock is representative for the most earthquakes in North China. Some informations probably to be usable for the predictions of earthquakes were discussed.