Abstract: The effect of different tempering processes on the mechanical properties of H11 hot-working die steel was studied by optimizing the heat treatment process. The experimental results show that the secondary tempering treatment,appropriately increasing the tempering time and reducing the tempering temperature, enhances the precipitation of fine and dispersed carbides, and can fully release the quenching stress, which contributes to the significant improvement of the strength,hardness, toughness and plasticity of H11 hot-working die steel. The optimized two-time tempering process at 600 ℃ for 2.5 h can increase the hardness of the steel by 12.1% compared with the traditional one-time tempering process. The yield strength and tensile strength are increased by 6.7% and 14.1%, respectively. The elongation and reduction of cross-section area are increased by 65.2% and 177.2%, respectively. The fracture toughness is increased by 48.2%, as well as the impact toughness is increased by 31.8% at room temperature. According to the analysis of tensile fracture morphology, there are a large number of dimples and secondary cracks in the specimens with optimized tempering process, and the fracture characteristics are typical ductile fracture.