The invention discloses high-heat-resistance and high-impact-toughness hot-work die steel for hot forging and a preparation method thereof, and belongs to the technical field of die steel. The die steel comprises the following chemical components, by weight ratio: 0.40-0.50% of C, 0.30-0.60% of Si, less than or equal to 0.006% of S, less than or equal to 0.01% of P, 0.60-0.9% of Mn, 1.80-2.80% ofMo, 3.00-3.80% of Cr , 0.40-0.60% of V, 0.80-1.40% of Ni, 0.3-0.6% of Al, 0.50-1.10% of Co, 0.002-0.008% of rare earth elements and the balance Fe and inevitable impurities. The preparation method comprises the steps that steel is subjected to smelting and ingot casting, after a prepared steel ingot is subjected to high-temperature diffusing heat treatment, multi-directional forging and hot working are carried out, controlled cooling after forging is carried out, microstructure homogenization is carried out, refining heat treatment is carried out, and isothermal annealing treatment is carriedout. The die steel has the advantages of being relatively high in heat resistance, impact toughness and hardenability and particularly suitable for manufacturing a hot-work die with high heat resistance and impact toughness and with the large cross section with the thickness of 400mm or larger.