The invention belongs to the field of metal material, and relates to a preparation method of a multielement alloy based on a tungsten-potassium alloy. The method comprises the following process steps: (1) in an argon atmosphere with the oxygen content of less than 0.1 ppm and the water content of less than 0.1 ppm, weighing a tungsten-potassium alloy powder, a metal X powder and grinding balls, together adding into a ball milling tank, vacuumizing the ball milling tank, then filling the ball milling tank with mixed gas of hydrogen gas and argon gas, and carrying out ball milling for 20-60 h, wherein the metal X is at least one of Ti and Y; and (2) loading the mixed powder obtained in the step (1) into a mould, then putting the mould loaded with the mixed powder into a spark plasma sintering furnace, sintering for 1-6 min under the pressure of 40-100 MPa and the temperature of 1600-1900 DEG C, then cooling to the room temperature along with the furnace, next reducing the pressure to the normal pressure, and thus obtaining the product. The multielement alloy prepared by the method has excellent irradiation resistance and thermal shock resistance.