In this paper, 2 kinds of commercial perfluoropolyether (PFPE) greases were coated on the polyimide (PI) blocks, which were placed within simulated space environment including atomic oxygen (AO), proton (Pr), ultraviolet (UV), and electron (El) irradiations, and then the tribological performance has been investigated with a ball-on-disc tribometer. Results indicated that the MoS₂-grease showed better lubrication performance than the PTFE-grease. The changes in infrared spectroscopy induced by Pr and El irradiations were more obvious than that by AO and UV irradiations. Results of energy dispersive X-ray spectroscopy indicated that Pr and El irradiations caused carbonation of greases, and AO and UV irradiations induced oxidation of greases. Referred to the tribological properties of PI coated with PFPE oil, PI coated with PFPE greases showed minor changes in friction coefficient and wear rate, and the MoS₂ additives could significantly improve the lubrication properties of PFPE greases in simulated space environment.