Abstract: H13 hot-working die steel was smelted by vacuum induction melting+vacuum arc remelting (VIM+VAR), electric arc furnace+ladle furnace+vacuum degasses+protective atmosphere electroslag remelting (EAF+LF+VD+PESR), EAF+LF+VD and EAF+LF+VD+electroslag remelting (ESR) processes, and then was treated with high temperature diffusion, rolling, austenitizing and tempering. The characteristics of non-metallic inclusions in H13 steel produced by different smelting processes and their effect on mechanical properties was studied. The results show that the tempered microstructure of the test steel produced by four smelting processes was composed of tempered martensite+undissolved carbide+precipitated carbide. The test steel produced by VIM+VAR process had the lowest content and small-sized non-metallic inclusions, indicating high cleanliness, which led to the best mechanical properties. The test steel produced by EAF+LF+VD process had the highest content and large size of non-metallic inclusions, and the carbide particle breakage appeared, resulting in the lowest plasticity of the steel. Small and few non-metallic inclusions were not easy to be crack sources to accelerate material fracture during the tension process, so higher cleanliness could improve the mechanical properties of H13 steel.