Abstract: Three point bending test was carried on the base metal and weld seam of X80 pipeline steel with design factor of 0.8, and then according to GB 2038-1991 standard to conduct the study of fracture toughness and failure assessment curves(the R6-3 failure assessment curve had constructed, as compared to R6-1 and R6-2 curves).The results show that the fracture toughness of X80 pipeline steel base metal and weld seam were 1 080 kJ·m-2 and 298 kJ·m-2 based on J-R resistance curves. The failure assessment curves of the base metal was more high than that of the weld seam when the load was high because of the base metal owing more high plasticity. Meanwhile, the R6-3 curve had the biggest safety range and the highest precision,these could accurately reflect the performance of the material, load type and shape of the components, also preferably played the performance of the material.