The water-lubricated polymer stern tube bearing is a key-component which has great influences on operational reliability and safety of marine power systems. The poor thermal conductivity and frictional heat generated by friction easily cause severe deforming behaviours on the polymer bearing contacting surfaces, and lead to the high coefficient of friction as well as fluctuations. Therefore, for figuring out the tribological properties of polymer matrix composites after being modified by nano-fillers and conducted aging treatments, an array of high density polyethylene (HDPE) composites composed with CeO2 were manufactured and tested on a commercial tribo-tester. The results showed that the CeO2 nano-particles had a significant effect on the anti-aging property of HDPE and affected its tribology properties. Compared with the pure HDPE, CeO2 nano-particles could reduce the COF after aging, and the COF reduction rate reached maximum to 46.6% after aging for 25 d. The CeO2 nanoparticles reduced the internal molecular chain fractures of the modified polymer under aging conditions, and slowed down the descending trends of the typical physical properties of polymer. The tribology properties of the modified polymer were enhanced by CeO2 nano-particles compared with the pure HDPE, and the reinforcement model was disclosed in the end. The knowledge gained herein will be useful for designing a new water lubricated bearing polymer with good anti-aging property for extending its applications under extreme circumstances.