The fracture toughness of material are affected by the constraint at crack tip. In order to assess the structural integrity of cracked structure accurately,it needs to obtain the constraint dependent fracture toughness. In this paper,based on the unified constraint parameter Apand the unified correlation line with fracture toughness,a determination method of constraint dependent fracture toughness of structure is proposed. Furthermore,the constraint dependent fracture toughness and fracture bending moment of pipeline with different crack lengths and depths are calculated. The results show that the fracture toughness and fracture bending moment are depending on the crack tip constraint closely,the crack with a/t = 0. 5 and a/c = 0. 5 ,0. 6 will fracture easily. This study is with great significance of developing structural integrity assessment which incorporates constraint effect,increasing the reliability of structure,and so on.