Abstract: Polyether ether ketone (PEEK) is promising for seawater-lubricated bearing applications but exhibits insufficient tribological performance in saline environments for high-load, high-speed conditions. This study investigated the effect of micro–nano synergistic reinforcement on the tribological behavior of PEEK by incorporating carbon fibers (CF) and multi-walled carbon nanotubes (MWCNTs). To enhance interfacial bonding and nanofiller utilization, the CF were surface-treated by two approaches: sizing with polyethylenimine (PEI) to improve fiber wetting and capture MWCNTs, and chemical grafting with a third-generation polyamidoamine (PAMAM) dendrimer to covalently attach MWCNTs to CF. Four materials—pure PEEK, CF-MWCNTs/PEEK, CF-PEI-MWCNTs/PEEK and CF-PAMAM-MWCNTs/PEEK—were prepared, and tribological tests were carried out in 3wt% NaCl medium under loads of 50-130 N and sliding speeds of 3-9 mm/s. The results showed that surface modification of the reinforcements markedly improved the composites’ tribological performance: PEI and PAMAM introduced amino groups onto the CF surface, which strengthened the interface with the PEEK matrix, improved the dispersion of MWCNTs, and promoted adsorption of Na⁺ from the solution to form a continuous, stable hydrated lubricating film that effectively suppressed corrosion–wear coupled failure. The PAMAM-modified system exhibited the best performance: its friction coefficient and specific wear rate were reduced by 16.1% and 54.6%, respectively, relative to pure PEEK, and by 9.1% and 36.5%, respectively, relative to the unmodified CF-MWCNTs/PEEK; it also maintained superior frictional stability and wear resistance across all tested conditions. In conclusion, CF surface modification with PEI or PAMAM is an effective strategy to enhance the tribological performance of PEEK-based composites in seawater environments.