Abstract: In accordance with the BS 7448,fracture toughness test standard,CTOD (crack tip opening displacement) tests were conducted at 0℃ in welded joints of X65 pipeline steel.According to the requirements of the standard,the specimen is a standard TPB (three point bending) shape that has a rectangular section of B×2B and notch orientation of NP.the results were calculated by using the P-V curves of parent material,weld metal and HAZ (heat affected zone).Finally,The test results were generalized and analysed.Especially,it indicates by the microstructure from metallograph that there are 3 HAZ specimens that don't meet the challenge that the fatigue crack tip is not more than 0.5mm from the fusion line and locates in coarse grain zone.The test results are in consistence with the P-V curves and CTOD values,explain the dispersity of the test values,and provide reliable evidence for ECA (engineering critical assessment),validate the BS7448 and embody its superiority.