The effects of heat treatment on the precipitates and strengthening mechanism in AISI H13 steel were investigated. The results showed that the presence of nanoscale precipitates favorably affected grain refinement and improved the yield strength. The volume fraction of precipitates increased from 1.05% to 2.85% during tempering, whereas the average precipitate size first decreased then increased during tempering. Contributions to the yield strength arising from the various mechanisms were calculated quantificationally, and the results demonstrated that grain refinement and dislocation density most strongly influenced the yield strength. In addition, under the interaction of average size and volume fraction, precipitates’ contribution to the yield strength ranged from 247.9 to 378.5 MPa. Finally, a root-mean-square summation law of σ = σ_g + σ_s +(σ_d~2 + σ_p~2)~(1/2), where σ_g, σ_s, σ_d, and σ_p represent the contributions of fine-grain strengthening, solid-solution strengthening, dislocation strengthening, and precipitation strengthening, respectively, was confirmed as the most applicable for AISI H13 steel, which indicates a strong link between precipitates and dislocations in AISI H13 steel. The effects of heat treatment on the precipitates and strengthening mechanism in AISI H13 steel were investigated. The results showed that the presence of nanoscale precipitates favorably affected grain refinement and improved the yield strength. The volume fraction of precipitates increased from 1.05% to 2.85% during tempering, while the average precipitate size first decreased then increased during tempering. the addition of under the temperate strength Finally, a root-mean-square summation law of σ = σ_g + σ_s + (σ_d ~ 2 + σ_p ~ 2) ~ ( 1/2), where σ_g, σ_s, σ_d, and σ_p represent the contributions of fine-grain strengthening, solid-solution strengthe ning, dislocation strengthening, and precipitation strengthening, respectively, were confirmed as the most applicable for AISI H13 steel, which shows a strong link between precipitates and dislocations in AISI H13 steel.