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Wear properties of TC4 alloy were systematically tested in air and vacuum (10-5Pa). The effects of load and sliding velocity on the wear rate of TC4 alloy were studied, and the microstructural analysis of the worn surface layer of TC4 alloy were carried out. In air, the microstructure of the surface layer presented slid band of dislocation at the lower sliding velocity, and micro-crack at the higher sliding velocity. In vacuum, the microstructure of the surface layer was refined to a gain size range of 50 nm~100 nm and comprised of high density of dislocations. Twins existed in the substructure of the surface layer at higher sliding velocities.