Abstract: The tribological properties of GF/PI and nano- TiO₂/GF/PI composites irradiated by atomic oxygen are studied in this paper. The influencing mechanism of atomic oxygen irradiation is discussed, and the structural analysis of the composite surface is carried out before and after the irradiation. It is found that atomic oxygen irradiation could destroy the matrix molecular chains in the composite surface, and change the surface structure of the composite. The friction coefficient of the PI composite is little influenced by atomic irradiation, which, however, tends to reduce the wear rate to some extent. The variation of tribological properties of PI composites induced by atomic oxygen irradiation might be due to the influence of the changed surface structure and composition on the transfer films formed on the counterpart steel rings.