Abstract: It was designed to change polymer conformation by adding poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) to 3 HEPES-glycerol solutions mixed with different volume ratio glycerol in this work for studying the effect of polymer conformation on tribological performance. Conformation change of polymer PLL-g-PEG was quantitatively characterized. Quartz Crystal Microbalance (QCM) was used to quantitatively characterize the change of polymer brush conformation with the addition of poor solvents. The results showed that the highly hydration effect of polymer brushes in good solvents played a critical role in improving the friction and wear, while the viscosity effect of glycerol was dominated in poor solvents. It was verified by nano-scale optical interference thin film measurement device that film-forming properties in the gap between the steel ball and glass disk, which were both grafted by polymer brush, was determined by both hydration effect induced by conformational change of the polymer brush and hydrodynamic effect. And the influence of hydration effect and hydrodynamic effect on film formation in contact changed with entrainment velocity. The water-based lubrication mechanism under the combined effect of the two was preliminary probed, which was very important for broadening the application of water-based lubrication.