Abstract: Abstract: This article uses laser self-fusion welding method to achieve welding of 10mm thick TA5 titanium alloy, and explores the relationship between the microstructure and mechanical properties of laser welded joint. Research has shown that laser self welding can achieve high-quality welding of TA5 titanium alloy, with continuous and uniform formation of the weld surface, and no obvious defects such as pores, cracks, and inclusions inside; The microstructure of the base metal consists of small and uniform equiaxed α phase and point like intergranular β phase. The center of the weld seam is mainly composed of coarse β columnar crystals, with small cross distributed needle like martensite inside the crystals; The microstructure of the coarse-grained region is mainly composed of primary block shaped α phase and needle shaped martensite α ´ phase, while the microstructure of the fine-grained region is mainly composed of equiaxed α phase, a small amount of needle shaped martensite α ´ phase, and residual β phase; Tensile fracture occurs at the base material far from the weld seam, which is directly related to the formation of needle like martensite, with an average tensile strength of 783 MPa; The microhardness of the laser welded joint is the highest at the weld seam, and the overall distribution is saddle shaped.