Abstract: 8418 steel is a type of air-hardening hot work die steel containing elements such as Cr, Mo, and V. It is widely used in hot forging dies, hot upsetting dies, stamping dies, die casting dies, and extrusion dies in the field of hot forming. This article takes the 8418 steel produced by a domestic forging company as the research object and studies the influence of heat treatment on the microstructure and mechanical properties of forged 8418 die steel using methods such as metallographic analysis, hardness testing, tensile testing, and impact testing. The study shows that after heat treatment（ultra-fine treatment and spheroidizing annealing, normalization at 880℃, quenching at 1030℃,and double tempering at 600℃）, the grain size grade of the material has been improved from the original 6.5 to 8.5,and the final microstructure is characterized by fine-grained tempered sorbite. The strength, hardness, plasticity,toughness, and impact performance of the material have all been significantly improved. The final heat-treated steel has a yield strength of 1660MPa, a tensile strength of 1800MPa, an elongation of 17.5%, a hardness of 564.7HV, and an impact energy absorption of ＞ 300J, demonstrating excellent comprehensive mechanical properties.