Abstract: The effects of reheat treatment on microstructure and properties of the bend pipe and straight pipe of X100 pipeline steel were studied by quenching them at 850, 950, 1 050, 1 150 ℃ and then tempering at 250, 350, 450, 550 ℃, or only tempering at 250, 350, 450, 550 ℃, respectively to gain the optimized technological parameters. The impact toughness was measured at different temperatures and the fracture morphology of samples before and after reheating treatment was analyzed. The results show that, when the steel was quenched at 950 ℃ and then tempered at 550 ℃, its microstruecture was B+PF+P, the hardness was moderate, the impact fracture exhibited good dimples in the fibrous region, radial region and shear zone, indicating a good match with the main pipe. When the steel was directly tempered at 550 ℃, the microstructure was homogenous, the hardness was moderate, also matched with the main pipe