Abstract: The tensile fracture delamination of a Q550D steel tensile sample occurred after tensile test. The causes of tensile fracture delamination were analyzed by means of macro observation, metallographic examination, hardness test and energy spectrum analysis. The results show that the unsuitable continuous casting process was adopted in the continuous casting process of Q550D steel slab, resulted in positive segregation at the upper and lower 1/4 of the continuous casting billet, negative segregation and inclusions at 1/2 of the continuous casting billet. After the subsequent rolling, there was a serious bainite segregation band at 1/4 of the thickness of the plate, and there were a large number of class B inclusions in the core area, which finally led to delamination in the fracture of the tensile samples.