Titanium alloys, which are favoured by the national defense industry for their excellent properties, such as low density, high specific strength and corrosion resistance, are used in tanks, armored vehicles, artillery and other weapons and equipment. However, owing to their low surface hardness and poor wear resistance, the application range of titanium alloys is limited. On this basis, the surface of the TC4 titanium alloy sheet was treated by ion nitriding to improve the surface hardness of the alloy and to explore the changes in microstructure and properties after nitriding. The microstructure after ion nitriding was observed via X-ray diffraction and scanning electron microscopy. The hardness of each sample was measured via a Vickers microhardness tester, and the effects of the ion nitriding process on the microstructure, structure and properties were analysed. The results show that the surface of the TC4 titanium alloy sample is golden yellow after nitriding at 450 ℃ for 8 h. The nitriding layer formed on the surface mainly contains a TiN phase with high hardness, which improves the surface hardness of the TC4 titanium alloy in both the plane and thickness directions, and the effect of increasing hardness in the thickness direction is more significant.