Multi-ion beam (MIB) surface modification techniques are used to treat Cr12MoV cold die work steel. The modified layers of steel treated by MIB is improved with low friction coefficient, high wearing resistance and strong adhesion with the matrix through results of hardness, scratch and wearing test. The modified layers include (Ti2N +TiN), (а-Fe+TiN) and (а- Fe(N)+Cr7C3) three layers from surface to inside by analysis of SEM, EPMA and TEM. And the surface layer presents nano-size grain refining. The service life of the Cr12MoV cold die steel treated by MIB can be prolonged 3-5 times longer than the untreated one.