Abstract: Based on level three programme (ductile tearing assessment)of assessment standard BS7910, ductile tearing assessment of surface flaw in circumferential weld of pipe-line under pure bending load was proceeded by using J integral engineering estimate method of SC.ENG.By taking X56 steel pipeline as an example, effects on assessment curve and evaluating results were given by flaw dimension and fracture parameter choosing were discussed, and the assessment point was put forward that J_mat is more reasonable than J_g in determining assessment points while choosing J integral parameter to make a ductile tearing assessment of flaw in metal structure.The research results are not only taken as a guide on safty evaluation in pipeline construction, but also can make engineering application of the ductile tearing assessment of structure with flaw more popular and referentia.