The invention provides a hard alloy surface boronizing method. The method comprises the following steps that (1), sand blasting treatment is performed on a hard alloy, and an oxide layer on the surface of the hard alloy is removed; (2), a boronizing agent is poured into a boronizing container, the hard alloy treated in the step (1) is buried into the boronizing agent, and then the boronizing container is closed and put into a sintering furnace, wherein the boronizing agent is composed of the following components, by weight percentage, 10-15% of a boron supply agent, 25-30% of an activator andthe balance a filler, wherein the boron supply agent is composed of equal weight of boron nitride and boron carbide; the activator is composed of equal weight of potassium fluoborate and tetrafluoroboric acid pyrrolidine salt; the filler is silicon carbide; and (3), the sintering furnace is vacuumized until the vacuum degree is 100 Pa, inert gas is injected into the sintering furnace until the pressure in the sintering furnace reaches 0.07 MPa, heating starts to be performed, heat preservation is performed for 2-6 hours after the temperature is increased to 1,100-1,300 DEG C, heating is stopped, and then the temperature is cooled to the room temperature. By the adoption of the hard alloy surface boronizing method, a boronizing layer formed by the method is large in thickness, and the hardness, the wear resistance, the bending strength and the toughness of the hard alloy can be effectively improved.