Based on the analysis of characteristics of aftershock activities in Ta-ngshan,the authors think aftershock activities in Tangshan can be fallen into four stages and three subregions.In this paper the authors also discu-ss the relationships between these characteristics and the geological struc-tures,the structure of depthin seismic focus area,and the characteristics of ground deformation before and after main earthquake.Finally,the aut-hors point out that new distribution of stress field after main earthquake and dilation-flowing fluid theory can regarded as a physical interpretati-on of genesis of Tangshan a ftershock.