Abstract: To investigate the microstructure and property characteristics of rotary friction welded joints of TC21 high-strength titanium alloy and further optimize the mechanical properties of the joints, the welded joints under different conditions were prepared. The mechanical properties, microstructure evolution and characteristics of the joints in as-welded and post-weld solution aging treated conditions were systematically studied. The average tensile strengths of the as-welded and heat-treated joints were 1 124 MPa and 1 163 MPa, respectively. The impact energy of the weld zone of the as-welded joint was 12.2 J, while that of the joint after solution aging treatment reached 29.2 J, representing an increase of 139%. A large number of acicular martensitic α' phases precipitated in the weld zone after welding, resulting in an increase in the microhardness of the weld zone. After solution aging treatment, the microstructure of the weld zone transformed into rod-like secondary α phases, grain boundary α phases and intragranular secondary α phases with fine structures. Compared with the as-welded state, the hardness of the weld zone decreased. The microstructure transformation of the weld zone after solution aging treatment improved the hardness uniformity of the joint. Moreover, the change in the morphology and size of α/α' phases significantly enhanced the impact toughness.