Friction film has an important influence on the tribological properties of C/C-SiC composites, which is closely related to its composition. In this study, exogenous third bodies in the form of powders of graphite, SiC, SiO2 and a mix of graphite, SiC, and SiO2 powders were added to the friction surface of the C/C-SiC composites under a constant speed. By comparing the change in the coefficient of friction (COF) and the wear rate of the C/C-SiC composites before and after addition of exogenous third bodies, the influence of each component on the tribological properties of the C/C-SiC composites and its mechanism were proposed. The graphite third body had a solid lubrication effect, with the average COF bellowing 0.344 and a 24% reduction in wear rate after addition. With the addition of SiC and SiO2 third body, the average COF was greater than 0.550 and 0.441, and the wear rate increased by 128.4% and 25.1%, respectively. SiO2 with a stronger pinning effect, promoted the formation of friction film and ultimately resulted in a smaller increase in average COF and wear rate. With the addition of the multi-component third bodies, the first platform containing SiO2 and SiC was formed, which resulted in a reduction in sharpness and being prone to refinement. Meanwhile, the large first platform accelerates the formation of friction film. Furthermore, while the first platform exceeded to the bearing capacity, SiC and SiO2 started to decompose, and redistributed in the friction film, which cause the instantaneous COF tended to stable with a low wear rate.