TC21 titanium alloy specimens after pretreatment were carburized in a vacuum carburizing furnace. The microstructure, phases, hardness and wearability of the carburized coating were analyzed by SEM, XRD, HV hardness tester and friction-wear test machine, respectively. Results show that after carburization, no hydride can be determined by carburized layer tissue, no hybrids or H-containing phase are observed in the coating, while TiC and other carbide phases appear. The hardness of the alloy surface after carburizing increases by 2.66 times. The friction coefficient of Ti/Ti is 0.6, after carburization that of TiC/TiC is 0.23, and that of Ti/TiC is between Ti/Ti and TiC/TiC. After carburizing treatment, frictional properties of TC21 titanium alloy are improved. When Ti/Ti part is grinding each other, the carburized part can improve the wear resistance. Wear of noncarburized part becomes serious when it is grinding with a carburized part. Carburizing also changes the friction state between TC21 titanium alloy components, i.e. from adhesion wear between Ti substrate and Ti ball, to grain wear and delamination wear between Ti substrate and TiC ball.