The invention provides a method for producing extra-pure high-speed tool steel. According to the method, materials are proportioned according to a target steel type, and industrial pure iron, metal chromium, metal tungsten and metal vanadium are placed into a crucible; metal aluminum, graphite blocks, industrial silicon and molybdenum-manganese-magnesium alloy are placed in a built-in sealing bin;after vacuumizing, the crucible is heated until the raw materials are molten down, and heat preservation is carried out after aluminum addition and deoxidation; the graphite blocks and the industrialsilicon are sequentially added, and the heat preservation is carried out; high-purity argon is introduced, and after the pressure is stable, the molybdenum-manganese-magnesium alloy is added for deepdeoxidation and alloying treatment; the casting temperature is controlled to be 1530 DEG C to 1535 DEG C; and after casting is completed, pressure maintaining and cooling are carried out for 20 minutes, gas is discharged, the crucible is cooled to the room temperature, a steel ingot is taken out, and therefore the extra-pure high-speed tool steel is obtained. According to the method, the molybdenum-manganese-magnesium alloy is used for deep deoxidation and desulfurization, the characteristics of refining structure, modifying inclusion and breaking carbide by magnesium in the alloy are strengthened, the effect of the magnesium is improved by utilizing the pressure, the extra-pure high-speed tool steel with the total oxygen content less than or equal to 0.0002% and the sulfur content less than or equal to 0.0005% is finally produced through smelting, and the plasticity and the toughness of the extra-pure high-speed tool steel are remarkably improved.