Abstract: The 60-mm thick Ti6321 plate is welded by the narrow gap welding with vibrating wire feeding, and the microstructure and mechanical properties of the welded joint studied. The results show that the narrow gap welded joints with vibrating wire feeding are well combined, and the microstructures of different areas in the welded joint are different. The weld zone microstructure of the cover layer of the welded joint is of bundles of long and fine α phases, the fusion zone is composed of acicular martensitic α' phase, residual β phase and α phase, and the heat-affected zone (HAZ) is composed of the acicular α phase, primary α phase with fuzzy grain boundaries and β phase. The weld zone of the filling layer of the welded joint has wider α phase, the degree of α beam dislocation in the fusion zone decreases, and the number of needle-like α phase in the HAZ near the weld zone increases. The microstructures of both the weld and fusion zones at the backing layer of the welded joint are interwoven martensite, and a large number of residual α phases with blurred grain boundaries are generated in the HAZ. The average hardnesses of the matrix and HAZ in the cover and filling layers are higher than those in the weld zone. The microhardnesses of the matrix weld zone in the backing layer are comparable and lower than that of HAZ. The tensile strength of the joint is above 860 MPa, and the joint performance has good consistency and uniformity. The tensile fracture shows good ductile fracture characteristics.