Abstract: In this study, numerical simulation analysis on fracture of girth welds on pipelines with crack defect and small Single Edge Notch Beam(SENB) was performed with the finite element method for accurately characterizing the correlation of apparent fracture toughness of the girth welds on high-grade steel pipelines and the small specimens. The conversion coefficient of apparent fracture toughness was introduced by comparing the difference of apparent fracture toughness of the girth welds on full-scale pipelines and the SENB specimens. Conversion coefficients between full-scale pipelines and SENB specimens under different working conditions were obtained by quantitatively studying the impact of pipe diameter, wall thickness, crack length and depth on the apparent fracture toughness of girth welds on full-scale pipelines, realizing quantitative characterization of the apparent fracture toughness of girth welds on high-grade steel pipelines based on the test results of small specimens. The results indicate that the pipe diameter has little effect on the apparent fracture toughness and its conversion coefficient. The conversion coefficient of fracture toughness increases with the increasing of wall thickness and decreases with the increasing of crack length and depth. The effect of crack depth on the apparent fracture toughness of pipelines is more obvious than other influencing factors. A relatively accurate apparent fracture toughness of girth welds on high-grade steel pipelines can be obtained based on the conversion coefficient, providing theoretical reference for accurately characterizing the apparent fracture toughness of girth welds on high-grade steel pipelines.