Abstract: A high-strength boron steel was tempered at 200-600℃ after rolling and quenching, and then the effects of tempering temperature on the microstructure and mechanical properties of the steel were studied. The results show that with the increase of tempering temperature, the microstructure of the tested steel changed from needle-like martensite to lath-like martensite. The strength and hardness decreased while the elongation increased and the impact energy first increased then decreased and then increased. The obvious phenomenon of tempering brittleness of the tested steel appeared after tempering at 300-400℃, which was mainly caused by the precipitation of Fe-C-B type compound at the grain boundary.