Abstract: The three-dimensional finite element model of linear friction welding (LFW) of TC4 titanium alloy was established on the basis of DEFORM software. The material flow behavior during the welding process was numerically simulated. The results show that the flow velocity of material near the edge of friction surface is bigger than that in the middle of friction surface. In the friction stage, the flow of material in the friction surface happens both parallel to and perpendicular to the vibration direction of weldment. In the forging stage, the material near edge line of friction surface undergoes big flow velocity and low temperature value, which makes the axial shortening of weldment increasing. The displacement of material perpendicular to the vibration direction decreases with the increase of distance away from the edge of friction surface, which shows that the self-cleaning of linear friction welding may happen in the whole friction surface only in the case of large axial shortening of weldment.