Carbon-based coatings have been successfully utilized in aerospace, automobiles, and ocean exploration, as typical solid lubricants. Particularly, amorphous carbon coatings (a-C:H) have been employed on kinematic pairs of advanced equipment, such as polyether ether ketone (PEEK)/steel pair, for enhancing their wear resistance and solid lubricity. However, the significant disparity in mechanical properties between PEEK and a-C:H and the poor interface adhesion strength are the key factors that limit the further improvement of tribological performance. In this study, based on the gradient transition of composition and mechanical properties between PEEK and a-C:H, a-C:H/a-C:H:Si:O functionally graded coatings (FGCs) were fabricated on PEEK. The friction behavior of the a-C:H/a-C:H:Si:O FGCs coated PEEK sliding against 304 stainless steel was performed in dry atmosphere using a ball-on-plate reciprocating tribometer. Compared with the single-layer a-C:H and a-C:H:Si:O coated PEEK, the friction stability period of FGCs is extended by at least 33%. When the thickness ratio of a-C:H/a-C:H:Si:O is 1/1, the wear rate of FGC is as low as 5.6×10 -7 mm 3/Nm. The excellent tribological performances of FGCs can be attributed to the appropriate mechanical property transition and strong adhesion strength between the coatings and the PEEK. The finite element simulation results indicate that the FGCs can provide more excellent deformation resistance and can also significantly eliminate stress concentration. This work can provide basic theoretical guidance for preparing functionally graded amorphous carbon coatings on PEEK to achieve excellent tribological and wear performance.