The invention particularly relates to high-impact toughness and high-thermal stability hot extrusion die steel and a preparation method thereof, and solves the problems of poor strength and poor heat thermal stability under low temperature due to lower carbon content of the conventional hot work die steel. The high-impact toughness and high-thermal stability hot extrusion die steel is prepared from the following raw materials in percentage by weight: 0.32-0.45 percent of C, 0.80-1.20 percent of Si, 0.20-0.50 percent of Mn, 4.75-5.50 percent of Cr, 1.00-1.75 percent of Mo, 0.80-1.20 percent of V, less than or equal to 0.018 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.30 percent of Cu, less than or equal to 0.55 percent of Ni+Cu, 0.04-0.10 percent of Nb and the balance of Fe and impurities. The high-impact toughness and high-thermal stability hot extrusion die steel and the preparation method thereof have the benefits that the thermal stability, the cold and hot fatigue resistance and the thermal wear resistance are improved under the situation that the high temperature strength and the high toughness are not reduced,, so that the service life of the die is greatly prolonged, therefore, the use cost is reduced.