Abstract: In order to improve the surface hardness and strength of Q345B structural steel, TiN-TiO₂ layered coatings were synthetically deposited on its surface by supersonic dual-filament arc spraying. Combined with XRD, XPS, SEM and EDS, the physical and elemental composition of the coatings, surface morphology and elemental diffusion behavior at the coating-substrate interface were analyzed. The Young’s modulus and hardness of the coatings were tested using a nanoindentation meter. The results show that the coating consists of TiN, TiO₂, and TiN_0.3, which has a dense coating structure,low porosity, and a certain thickness of metallurgical bonding zone at the interface. It also exhibits very high hardness of 26.3GPa and high Young’s modulus of 251.3 GPa, and the hardness is 10 times of that of Q345B structural steel substrate.