Abstract: This paper describes the structural profiles showing the main boundaries of earth crust and upper mantle, such as the boundary of granitic layer (G), the Conrad boundary (C), the Moho discontinuety (M) and the boundaries M₁ and M₃ in the upper mantle. They are constructed by using a method of converted seismic waves in the Be-ijing-Tianjin-Tangshan region.Three of them show the existence of a deep-seated structure zone of WNW trend in the study region. Along this zone uplifted boundary G, concaved boundaries of M₁ and M₃ in the upper mantle and thicked basaltic layer exist.The comparision of deep-seated structures with the distribution of earthquake epicenters in this region indicates that most of strong earthquakes occurred at the crossings of WNW trending and NE trending structural belts, where the depth of boundaries G, M₁ and M₃ has a sharp change. And the hypocenters of these strong earthquakes are located in granitic layer.