Abstract: In this paper,the statistic analysis has been made for the distribution of focal depth based on the data of 8935 earthquakes in the Tangshan area,spanninng from 1976 to 1981.The results obtained show that there are not the same in a magnitude and its distribution is closely correlated with the crustal structure.Increasing earthquake depth gradually varies from NE to SW.The earthquake fault belt,which has an.angle of about 8?with the horizontal plain in the lower part and is in accordance with relief boundary in the upper,passes through the crust and down to the Moho.