Abstract: Linear friction welding of TC4 to TC17 titanium alloys was conducted,and the joint establishment and weld microstructure was analyzed. The interface temperature in the dynamic equilibrium phase was measured. The results show that large wear particles were easily generated in the interface in the initial phase. During the transition phase,the large wear particles were expelled from the rubbing interface and high temperature plasticized layer formed. Then the viscoplastic metal homogeneously moved out of the rubbing interface and formed a flash, and the grains on both sides of the interface were refined. It was observed that the temperature during the dynamic equilibrium phase exceeded 1 200℃,higher than the phase transition temperatures of both base materials,which led to the generation of recrystallized β grain,and then widmanstatten structure by α-β transformation. The microstructure in the thermal-mechanically affected zone (TMAZ) was apparently deformed and elongated.