Abstract: The NM450 low alloy wear-resistant steel was quenched online after hot rolling and tempered at different temperatures (200,250,300,350 ℃). The effect of tempering temperature on the microstructure and properties of test steel was studied. The results show that the microstructure of the tempered test steel at different temperatures was tempered martensite + bainite + residual austenite. With the increase of tempering temperature, the interface of tempered martensite slat gradually disappeared, the amount of carbides in the tempered martensite matrix increased, and the dislocation density and residual austenite content decreased. With the increase of tempering temperature, the yield strength, tensile strength and hardness of the test steel all decreased, the elongation after fracture decreased first and then increased, and the wear mass loss increased. The tensile fracture mode of the test steel tempered at different temperatures was ductile fracture. A large number of furrows appeared on the wear surface of the test steel when the tempering temperature was 200 ℃ and 250 ℃, and a large number of wear chips; fatigue cracks appeared on the wear surface when the tempering temperature rose to 300 ℃ and 350 ℃; the wear mechanism changed from plastic deformation to plastic deformation and fatigue wear.