In this paper, the linear friction welding of TC21 titanium alloy was investigated. The microstructure evolution of each region of the joint was analyzed by OM and SEM. The microhardness and tensile properties of the joint were tested. The results showed that a sound weld joint can be obtained using LFW. The joint was obviously divided into base metal zone(BM), thermo-mechanically affected zone(TMAZ) and weld zone(WZ); during the welding process, phase transformation and dynamic recrystallization took place in WZ, forming fine recrystallized grains, lath α precipitated at grain boundary, acicular martensite α phase precipitated inside grain,and a few residual α phase reminded at room temperature. Away from the weld center,the degree of recrystallization gradually decreased and the proportion of a phase gradually increased,the grain size gradually increased from the weld center to the end of flash. Due to the different of flash formation phase and cooling rate after welding. The microhardness of TC21 titanium alloy linear friction welded joint is arched,and the maximum value of microhardness in weld center is 460HV. The tensile test results indicated that the strength of the joint is equivalent to that of the base metal.