Abstract: Butt welding tests of 2 mm thick TC4 titanium alloy sheets were carried out by laser welding. The forming quality of the weld and the microstructure and tensile properties of the joint were studied under diffferent conditions （laser power density of 1.10×10⁶ W·cm⁻², laser heat input ranging from 500 J·cm⁻¹ to 700 J·cm⁻¹; laser heat input of 600 J·cm⁻¹, laser power density ranging from 0.88×10⁶ W·cm⁻² to 1.24×10⁶ W·cm⁻²）, and the tensile fracture mechanism of the joint was analyzed. The results show that the weld formation quality of TC4 titanium alloy joints prepared under different processes was good. The welds were all X-shaped, and the fusion widths of the upper and lower surfaces of the weld were similar. With the increase of laser power density or the decrease of laser heat input, the height of the weld waist decreased. Under different processes, the weld of the joint was composed of coarse β-columnar crystals and net-like α′ acicular martensite. With the increase of laser power density or the decrease of laser heat input, the degree of grain refinement in the weld was improved, and the amount of net-like structure increased. As the laser power density increased, the tensile strength of the joint first decreased, then increased, and then decreased. As the laser heat input decreased, the tensile strength first increased and then decreased. Under the laser heat input of 600 W and laser power density of 1.17×10⁶ W·cm⁻², as well as under the fixed laser power density of 1.10×10⁶ W·cm⁻² and laser heat input of 550 J·cm⁻¹, the height of the weld waist was close to half of the thickness of the alloy sheet, the degree of grain refinement of the weld was relatively high, and the amount of secondary α′ acicular martensite was relatively large; the tensile strength of the joint was relatively high, being 1 126, 1 041 MPa, respectively. At this time, the joints all fractured at the weld in tension, and the fracture mechanism was brittle fracture.