Abstract: TiN diffusion layer was prepared on Q235 steel surface by using double glow plasma surface alloying technique. The microstructure, hardness, composition, phase structure and corrosion resistance in NaOH solution of the layer were studied. The results show that the diffusion layer had a gradient structure, which was composed of diffusion layer with evenly distributed TiN particles and TiN deposition layer. The surface morphology of TiN layer was cell shape. The golden yellow TiN grains were compact and uniform. The thickness of the layer was 16 μm. A metallurgical bonding layer was obtained between the layer and the matrix. The atom ratio of Ti and N of the TiN diffusion layer surface was 1∶1, and the surface microhardness was 3 120 HV. The strongest diffraction peak intensity of TiN (111) in the TiN diffusion layer had obvious preferred orientation. In 4% NaOH solution corrosion resistance of the TiN diffusion layer was increased by 26.8 times compared with the Q235 steel and as well as 1Cr18Ni9Ti stainless steel.