Experiments on compact tension(CT),single edge-notched bending(SEB) and C-shaped inside edge-notched tension(CIET) specimens for pressure vessel steel SA-508 by using normalization method are carried out. The resultedJ-Δacurves are affected by specimen configurations and crack sizes,which is essentially owing to the different crack front constraint effect of specimen.J-Q-Mthree-parameter theory is introduced to qualify the crack front constraint effect,and weight average method is applied to solve the distance-independent constraint parameterQ. Finite element analyses show that,the parameterQ is load-independent under plane strain condition,but it is still influenced by load level under 3D condition. The size requirements ofJ-Q-Mdominance for three types of specimens have been constructed. Furthermore,by combining the experimental conditional critical toughnessesJ_0.2BL, J_0.5BL andJ-Q-Mapproach,the constraint-correctedJ-resistance curves are established based on the parameterQ,these curves can be applied to predict the ductile fracture behavior for any specimen and actual flawed structures.