The invention discloses a new method for surface boriding of hard alloy, which sequentially comprises the following steps of: removing an oxidation layer on the surface of the hard alloy; embedding the hard alloy into a solid boriding agent, putting the mixture into a nearly-closed boriding container, and putting the container into an induction heating furnace; vacuumizing the furnace, stopping vacuumizing until the vacuity is over 100 Pa, and filling inert gas or hydrogen; after the gas in the furnace reach the pressure, starting to perform induction heating to reach the boriding temperature of between 800 and 1,300 DEG C, and performing heat preservation for 0.5 to 8 hours to realize gas-solid phase boriding. The solid boriding agent comprises the following components in percentage by weight: 5 to 50 percent of boron supply agent, 2 to 40 percent of activating agent and the balance of fillers, wherein the boron supply agent is one or more of powdered B4C, BN and amorphous boron; the activating agent is two or more of powdered KBF4, NaBF4, NH4BF4, (NH4)2CO3, rare earth oxide and Mg powder, and one of the mixture is an activating agent containing a B element; and the filler consists of graphite powder granules and SiC powder or Al2O3 powder. Through the method, the boriding thickness of sintered hard alloy blank is more than 0.1 millimeter and is close to 1 millimeter, so the surface abrasion resistance of the hard alloy is improved greatly.