Abstract: The friction and wear tests of the perfluoropolyether (PFPE) grease-lubricated 2Cr13 steel friction pair with different sliding time were conducted on a pin-on-disk type tribometer in vacuum. The morphologies of the worn surfaces were observed by scanning electron microscopy.The chemical states of typical elements on the worn surfaces and PFPE grease were examined by means of X-ray photoelectron spectroscopy. The chemical structure of grease before and after wearing was analyzed by Fourier transform infrared spectroscopy. Experimental results show that the wear mechanisms of PFPE grease-lubricated 2Cr13 steel showed a transition from a mild wear including a mild cutting and a corrosive wear to a severe corrosive wear and a mild local delamination, then to a severe mixed wear involving with a severe adhesive wear and a local delamination with increasing the sliding time. The PFPE grease occurred physical degradation during wearing in vacuum, namly change in the ratio between the thickener and the base oil of the PFPE grease. Tribochemical reactions occurred between the PFPE grease and 2Cr13 steel during wearing in vacuum to produce FeF₃. The quantity of FeF₃ as a catalyst was too low to promote the chemical degradation of PFPE grease.