Abstract: Crack-tip constraints of pipe structures and laboratory single edge-notched bend (SENB) specimen, compact tension (CT) specimen, single edge-notched tensile (SENT) specimen and centre-cracked tension (CCT) specimen with different dimensions of initial cracks were characterized by finite element simulation method using the unified constraint parameter A_p, and the matching of crack-tip constraints between pipe structures and laboratory specimens were built. The results show that the matching of crack-tip constraints between pipe structures and SENB specimens, CCT specimens was poor. The crack-tip constraint of pipe structure with a/c=0.2, a/t=0.5 (a representing deep of crack, c representing half length of crack, t representing wall thickness of pipe) was similar to that of the CT specimen with deep cracks (a/W=0.7, W representing width of specimen); the crack-tip constraint of pipe structure with a/c=0.8, a/t=0.5, 0.8 was similar to that of the CT specimen with deep cracks (a/W=0.5,0.6 and 0.7). The crack-tip constraint of pipe structures was similar to that of SENT specimens, their crack-tip constraints matched very well. During the integrity assessment of actual structures, the laboratory specimen with the similar constraint to actual strcutre could be selected to carry out fracture mechanical experiments, and the assessment accuracy could be improved when the actual structure was assessed by the measured fracture mechanical properties.