Abstract: The effects of different quenching and tempering processes on the microstructure and mechanical properties of4Cr2Mo3WV die steel were studied by means of microstructure observation, hardness test and impact test. The results show that the microstructure of quenched 4Cr2Mo3WV steel is mainly acicular martensite. With the increase of quenching temperature, the size of acicular martensite in the test steel increases gradually, and the strength and toughness of 4Cr2Mo3WV steel quenched at 1060 ℃ is the best matched. The 4Cr2Mo3WV steel quenched at 1060 ℃ is tempered at different temperatures, with the increase of tempering temperature, the hardness of test steel increases first and then decreases, and the impact power decreases first and then increases. 1060 ℃ quenching +600 ℃ tempered test steel has the best matching of strength and toughness.