Abstract: TC4 alloy was welded by linear friction welding process. Microstructure of the joint was analyzed, and microhardness distribution of the joint was tested. The results showed that the welded joint can be divided into three zones: base metal zone, thermo affect zone (TMAZ) and weld zone. The microstructure of TMAZ are consist of equiaxed α and lamellar (α+β) be elongated in forced direction, fibrous and recrystallized(α and β) microstructure, acicular α′ and a little recrystallized α from near base metal to weld center. The microstructure at the weld zone is acicular α′. The size of α′ gradually becomes thicker from center to edge. The microhardness gradually increases from about 360 HV to 390 HV from the center to base metal in the direction perpendicular to the weld seam. Longitudinal microhardness of the weld zone gradually reduces to about 330 HV from the center to edge.