Abstract: Narrow gap laser welding of TC4 titanium alloy was carried out with stranded solid wire, microstructure and morphologies of welded joints were analyzed, and mechanical properties of welded joints, such as microhardness, tensile properties at room temperature and impact strength, were tested. The results showed that weld cross section was well formed without obvious defects such as incomplete fusion and porosity. Base metal was composed of equiaxed α+β phases. Grains of heat-affected zone were larger than those of base metal, heat-affected zone consisted of acicular α′ martensite + primary α phase, and weld was composed of coarse primitive β columnar grains and inner basket α′ martensite. Average tensile strength of welded joints was 940 MPa. Tensile fracture located in base metal, and dimple of fracture was shallow, whose main characteristic was ductile fracture. Average microhardness of weld was 375 HV, which was higher than that of BM and HAZ.Highlights: Laser welding with filler wire was carried out on 20 mm thick TC4 titanium alloy plate with high melting efficiency stranded welding wire as filler metal, and distribution law of microstructure and performance of welded joints of thick plate titanium alloy was explored, which provided basic data support for practical application of welded structure of thick plate titanium alloy.