The failure accidents in girth weld of pipelines occur frequently due to the combination of internal defects and external loads. However, the research on the fracture behavior of girth weld defects is relatively poor at present. To solve this problem, the cracking behavior and strain evolution law of the inner wall defects of the pipe girth weld are studied in combination with full-scale tests (FST). The constitutive and Gurson-Tvergaard-Needleman damage parameters of the pipe base metal zone, weld zone and heat-affected zone (HAZ) are calibrated through the small punch test (SPT) and single edge notch bending (SENB) test. On this basis, the welded pipe model with inner wall defects is established, and a numerical simulation method for dynamic fracture behavior based on damage mechanics is formed. The numerical simulation method is verified by FST data and theoretical calculation. The results show that the numerical results are consistent with the FST and theoretical calculation in the elastic stage, plastic stage, and fracture stage, and the error is within 10%. The novel numerical simulation method is provided as a means for the fracture behavior research of pipeline girth weld.