Pipeline girth welds are recognized as the weakest link in oil and gas transmission pipelines. Given the complex pipeline laying environment in China, the combined effects of additional external loads and internal working pressures can lead to stress concentrations in the girth weld region, significantly increasing the risk of pipeline failure. Currently, the standard inversion method is used as the primary tool within the industry to predict the ultimate load of pipeline girth welds. However, relatively conservative predictions are yielded by this method, and it is only applicable to conventional operating conditions. To achieve a more accurate prediction of the ultimate load of pipeline girth welds, detailed material mechanics tests were conducted on X80 pipeline girth welds, and the Gurson-Tvergaard-Needleman(GTN) damage parameters were calibrated using the finite element inverse calibration method. Based on these parameters, the GTN damage model and sub-modeling technique were employed to simulate the damage and failure process of full-scale pipeline girth welds containing crack defects. The ultimate load of the pipeline girth welds under complex loading conditions was yielded by this simulation. Finally, the simulation process was experimentally validated, revealing a 3.1% error in the predicted ultimate internal pressure and maximum and minimum prediction errors of 3.15% and 1.10%, respectively, for the far-field strain values at the time of crack fracture. The comparative results demonstrate that the proposed method for predicting the ultimate load of full-scale pipeline girth welds can accurately predict the ultimate load under complex loading conditions, making it suitable for the safety assessment of pipeline girth welds.