Elevated-temperature wear tests under atmospheric conditions at 400 ℃ were performed for a hot working die steel H21 on a pin-on-disk wear tester.The phase and morphology of worn surfaces were examined using XRD and SEM,and the relation of wear resistance to tempered microstructures was studied for H21 steel.XRD patterns exhibit that oxidative wear is a predominated wear mechanism with Fe3O4 and Fe2O3 on worn surfaces.It is found that with increasing normal load,obvious plastic deformation of substrate appears on worn surfaces.Microstructures start to affect apparently wear resistance of the steel with an increase of load.Under loads of 50-100 N,wear losses of steel retain low values and relatively approach for steels with various microstructures.As loads are increased to 150-200 N,wear losses of steel start to increase obviously and present apparent difference for steel with various microstructures.Wear resistance is found to increase in the sequence as follows:tempered sorbite,tempered martensite,tempered troostite without secondary hardening and tempered troostite with secondary hardening or upcoming one.Higher strength and microstructural stability are required for steels with excellent wear resistance. Elevated-temperature wear tests under atmospheric conditions at 400 ° C were performed for a hot working die steel H21 on a pin-on-disk wear tester. The phase and morphology of worn surfaces were examined using XRD and SEM, and the relation of wear resistance to tempered microstructures was studied for H21 steel. XRD patterns exhibit that oxidative wear is a predominated wear mechanism with Fe3O4 and Fe2O3 on worn surfaces. It is found that with increasing normal load, obvious plastic deformation of substrate appears on worn surfaces. Microstructures start to affect apparently wear resistance of the steel with an increase of load. Under loads of 50-100 N, wear losses of steel retain low values ​​and relatively approach for steels with various microstructures. As loads are increased to 150-200 N, wear losses of steel start to increase obviously and apparent apparent difference for steel with various microstructures .Wear resistance is found to increase in the sequence as follows: tempered sorbite, temp ered martensite, tempered troostite without secondary hardening and tempered troostite with secondary hardening or upcoming one. Heavy and microstructural stability are required for steels with excellent wear resistance.