Abstract: Water-based lubricants have excellent cooling performance and are widely used in metal processing and other fields. But the lack of extreme pressure and anti-wear performance,the application of water-based lubricants under heavy loads is limited. The tribological properties of three polymeric ester extreme pressure additives with different relative molecular mass were studied through friction and wear experiments. The experimental results show that the three water-soluble extreme pressure additives can improve the extreme pressure performance of water-based lubricants,among which the maximum non-seize load value of medium relative molecular mass and high relative molecular mass reaches up to 1 961 N at the mass fraction of 2.5%. The results of anti-wear and friction reduction performance test show that the minimum diameter of the wear spot of low relative molecular mass is 0.612 mm,and the wear mark is the shallowest,and the friction coefficient of high relative molecular mass is the most stable.