A ball-on-disk tribometer was employed to evaluate the lubrication performance and mechanisms of innovative TiO2 nano-additive water-based lubricants. Two experimental methods were applied to determine the optimal mass fraction of TiO2. In the method I, lubricants were added onto the worn disk tracks at a predetermined time interval. In the method II, the disks were immersed in the lubricants continuously during the whole process of tribological tests. The results both indicate that the water-based lubricants can significantly reduce the coefficient of friction (COF). The 0.8 wt% TiO2 lubricant demonstrates excellent tribological properties including the lowest COF and the strongest wear resistance under all lubrication conditions. The lubrication mechanisms are attributed to the rolling and mending effects of the TiO2 nanoparticles.