Abstract: The hardenability of ANSI 4130 steel and the effects of heat treatment process on its microstructure and mechanical properties were studied by adjusting quenching temperature. The results show that the quenching microstructure is martensite and a small amount of residual austenite, the hardened layer depth of the material is about 20 mm. In addition, the hardness fluctuation from surface to interior is relatively small at the quenching temperature of 860 ℃, and the average hardness of the center is about 41 HRC. After tempering at 660 ℃, the microstructure of test specimens with different quenching temperatures is mainly tempered sorbite. After quenching at 860 ℃ and tempering at 660 ℃, the mechanical properties of the material are optimal with the hardness of 229 HBW, the yield strength of 548 MPa, the tensile strength of 727 MPa, the area shrinkage of 68%, the elongation of 21%, and the impact energy of 140.8 J.