Abstract: Ni-P co atings were prepared on the surface of TC6 titanium alloy by electroless plating method, and were modified by heat treatment at 200 ℃, 300 ℃, 400 ℃ and 500 ℃, respectively. The tribological properties of Ni-P coating in4109 lubricating oil and air were investigated. The results show that the hardness of Ni-P coating increases first and then decreases, and the highest hardness of the coating reaches 980.5 HV at 400 ℃. Meanwhile, the crystallization process of Ni-P coating basically completes at 400 ℃. When the temperature rises to 500 ℃, Ni is grown at the expense of Ni₃P, and Ni₃P is partially transformed into Ni₂P. The wettability of 4109 synthetic lubricating oil on the coating surface increases first and then decreases with the increase of heat treatment temperature, and the lowest contact angle is 9.86° at 400 ℃. The friction coefficient decreases gradually with the increase of hardness. The lowest friction coefficient of 400 ℃ heat-treated coating is 0.15 in lubricating oil, which is only 20% of friction coefficient for TC6 substrate in air medium. The wear rate decreases first and then increases. Notably, the wear rate of coating treated at 400 ℃ is lowest in lubricating oil environments, measuring 2.8×10^-10 mm³·N^-1·mm^-1. This represents only 0.031% of the wear rate of initial TC6 titanium alloy in air. In the air medium, the wear mechanism of the TC6 substrate and the nickel plating of the substrate are mainly manifested as adhesive wear, while the wear mechanism of the nickel coating layer changes into the coexistence of plough wear and adhesive wear. Under the lubricating oil medium, all the samples mainly show the law of plough wear.