Abstract: Throgh adjusting alloy element content on the basis of the composition of Cr-Mo-B series NM450 steel, the 20 mm thick NM500 wear resistant steel plate was prepared by clean steel production technology and rolling process, and then was quenched and tempered. The microstructure and properties of the test steel at different quenching temperatures (880,900,920 ℃) and tempering temperatures (200,250,300,350,400 ℃) were studied, and the best heat treatment process was obtained. The results show that with the increase of quenching temperature, the undissolved ferrite in the test steel microstructure decreased, the austenite grain size first decreased and then slightly increased, the tensile strength, −20 ℃ impact absorbed energy and surface hardness all increased, and the percentage elongation after fracture decreased. In addition to the surface hardness after quenching at 880 ℃ did not meet the standard requirements, the mechanical properties of the test steel under other conditions met the standard requirements. After quenching at 920 ℃, with the increase of tempering temperature, the decomposition of martensite accelerated, the carbon content soluted in the matrix decreased, the number of carbides increased, the strength showed an overall decreasing trend, the percentage elongation after fracture first decreased, then increased and then decreased, and −20 ℃ impact absorbed energy and surface hardness both decreased. After bending test, only the 200 ℃ tempered sample did not fracture and there were no microcracks on the surface. The wear mass loss after tempering at 200 ℃ was significantly less than that after tempering at 400 ℃. After quenching at 920 ℃ and tempering at 200 ℃, the test steel had the best comprehensive mechanical properties with surface hardness of 496 HBW, tensile strength of 1 552 MPa, percentage elongation after fracture of 15.0%, −20 ℃ impact absorbed energy of 46 J, and qualified 180 ° cold bending property, and the properties all met the requirements of GB/T 24186—2022 standard.