Abstract: To solve the defects of low surface hardness, poor wear resistance and high friction coefficient of TC4 titanium alloy, gas nitriding was adopted in this study to carry out surface modification on powder metallurgy TC4 titanium alloy. The effects of nitriding temperature and holding time on surface phase composition, microstructure, microhardness and wear resistance of TC4 alloy were systematically investigated. The results indicate that the nitride layer on the alloy surface becomes thicker with the increase of nitriding temperature and holding time. The optimal comprehensive properties are obtained after gas nitriding at 900 °C for 3 h. A uniform nitride layer with the thickness of 15~20 μm is formed on the sample surface, which is dominated by Ti2N phase. Under this process condition, the maximum surface hardness reaches 872 HV0.2, which is 1.67 times that of the substrate. The average friction coefficient drops from 0.576 to 0.248 with a reduction of 56.9%, and the wear resistance is greatly enhanced. Consequently, gas nitriding can effectively improve the insufficient surface properties of powder metallurgy TC4 titanium alloy and provide feasible technical support for its engineering application under high-load friction service conditions.