Abstract: In accordance with the BS7448,fracture toughness test standard,J Resistance curve tests were conducted with the multiple specimen at -5℃ in welded joints of X56 pipeline steel.According to the standard,the specimen with fatigue precrack is a standard three point bending shape that has a rectangular section of B×2B(B:specimen thickness) and notch orientation of thickness direction.And then based on the double P-V(P:load,V:displacement) curves of each weld metal and HAZ(heat affected zone) specimen obtained from the two notch opening displacement,the load line displacement and the value of J were calculated.Finally,the paper determined the best fit curve through the valid data points,and got J_0.2 at all fatigue crack tips locating in HAZ by analyzing the fracture section of HAZ specimen,so the test results of HAZ are reliable.The BS-7448 Part 4,the standard on metallic materials,was applied to establish J-R curves of welded joints.Test results provide reliable evidence for engineering critical assessment.