Abstract: The fracture toughness test of pipeline girth weld is the basis of pipeline integrity assessment, and the accurate calculation of J-integral plastic factor is the premise of fracture toughness test. In this paper, aiming at the SENT (single edge notch tension) specimen with thickness-to-width ratio B/W=2, a three-dimensional finite element model of the SENT specimen of the pipe base metal with/without side grooves depth of 10% is established. The influence of crack length, specimen thickness, hardening index and specimen side groove on J-integral plasticity factor are studied. Through fitting the numerical analysis results after considering the factors such as crack length and material hardening performance, the J-integral plastic factor equations of SENT specimens are developed, which is suitable for pipe base metal with or without side groove of depth of 10%. The equations could be used to test the fracture toughness of SENT specimens.