Abstract: Based on the development requirements of advanced aircraft components, for TC21 titanium alloy linear friction welded joint, three heat treatment systems were designed, and the microstructure and mechanical properties of the joint were analyzed under the welding condition and different heat treatment conditions. The results show: the weld zone of the as welded sample is composed of fine β grains, and acicular martensite with a large number of dislocations precipitated in the crystal,which plays a role of dislocation strengthening, the microhardness is significantly higher than that of the base metal. The secondary α phase dissolved in the thermal mechanical affected zone which near the base material, resulted in decrease in microhardness. The α phase in the joints changes significantly after heat treatment. A long holding time of annealing in high temperature zone leads to the growth of primary strip α phase, and annealing in low temperature zone promotes the precipitation of secondary needle α phase. All tensile specimens after heat treatment are broken in the base material area, the microstructure of weld zone and thermo-mechanically affected zone of the joint after double annealing is β transformed tissue + primary strip α phase + secondary acicular α phase, the microhardness of each region is basically the same as that of the base metal, and the microstructure is more uniform.