In the paper the microstructure and properties of surface coating for Cr12MoV steel treated by TD (Thermal Diffusion) salt-bath vanadizing process are investigated. The research results indicate that after treated by the TD salt-bath vanadizing at 1223K for 5h and followed by oil quenching, and aged at 453K for 2h, the Cr12MoV steel could obtain a surface coating whose thickness is about 11.4um. The coating is mainly composed of vanadium carbide, and its thickness and microstructure are uniform and compact, respectively. At the same time, the coating obtained exhibits super-high surface microhardness, 2586HV. Then the wear resistance property of Cr12MoV steel is improved drastically. In addition, the research results reveal that the effect of TD salt-bath vanadizing treatment on the surface roughness of Cr12MoV steel is not obvious.