Tungsten disulfide-polydopamine-copper (WS2-PDA-Cu) nanocomposites were first prepared by a green and effective biomimetic strategy and then were used as a lubricant additive in polyalkylene glycol (PAG). The biomimetic strategy is inspired by the adhesive proteins in mussels. WS2 nanosheets were decorated by uniformly dispersed Cu nanoparticles (Cu NPs). The WS2-PDA-Cu nanocomposites with good dispersion stability, showed better friction reducing and anti-wear properties than did WS2, Cu NPs and WS2-Cu dispersed in PAG base oil. The average friction coefficient and wear volume were reduced by 33.56% and 97.95%, respectively, at 150 °C under a load of 100 N for the optimal concentration of 0.9 wt%. The lubrication mechanism was discussed.