Abstract: The quenching and tempering tests of 30CrNi2MoV steel at different temperatures were carried out. The effects of different quenching and tempering temperatures on the microstructure and mechanical properties of 30CrNi2MoV steel were studied by OM, SEM, TEM, tensile test and impact test. The results show that with the increase of quenching temperature, the amount of coarse carbides in 30CrNi2MoV steel gradually decreases and the grain size increases. The carbides in 30CrNi2MoV steel quenched at 880 ℃ basically dissolve into the matrix, the grains do not grow obviously, and the strength and toughness reach the highest. The optimum quenching temperature of 30CrNi2MoV steel is 880℃. The30CrNi2MoV steel quenched at 880 ℃ is tempered at different temperatures, with the increase of tempering temperature, the quantity of carbide in 30CrNi2MoV steel increases and its size increases. Secondary hardening occurs in 30CrNi2MoV steel tempered at 560℃. With the increase of tempering temperature, the tensile strength of 30CrNi2MoV steel increases slightly at first and then decreases gradually. The elongation basically has no significant change, and the impact absorption energy increases gradually. The tensile strength of 30CrNi2MoV steel tempered at 640℃ is 1204 MPa, the impact absorption energy is 118 J, the elongation is 16.8%, and the strength, plasticity and toughness are well matched. The optimum tempering temperature of 30CrNi2MoV steel is 640 ℃.