Impact toughness and its low-temperature transformation are key indicators of high-speed railway axle materials, which are closely related to the microstructure of the material. The embrittlement degree of materials with different microstructures at low temperatures also varies. Aiming to find a way to optmize the strength-toughness relationship of the relevant steel, the effect of adjusting the tempering temperature on the strength-toughness relationship of DZ2 steel, which was newly designed and developed at home for high-speed railway axle, was studied via tensile tests, room- and low-temperature impact tests, as well as observation and analysis of the microstructure evolution of the steel. Then the performance changes of the steel during the tempering treatment process were explained. The results indicate that as the tempering temperature increases, the tensile strength gradually decreases from 1357 MPa to 761 MPa, the elongation after fracture increases from 11.7% to 28.4%, the room temperature impact energy gradually increases from 34.3 J to 98.7 J, and the low temperature impact energy gradually increases from 24 J to 90.3 J. However, the impact of temperature reduction on the impact energy gradually weakens, the minimum impact energy decrease percentage of low-temperature is 8%. The transformation trend of these properties is closely related to the micro-scale deformation mechanism changes caused by the gradual spheroidization of carbides. It can be concluded from the comprehensive analysis that, while meeting the requirements of room temperature mechanical performance standards, adjusting the tempering temperature can improve the low-temperature impact toughness of the axle steel, to meet the needs of further high-speed railway speed increase and safe operation in harsh environments.