Abstract: Response surface method was used to optimize welding parameters of flat-top beam laser transmission welding of glass fiber reinforced PBT composites. Welding parameters (laser power, welding speed and glass fiber content) were selected as influence factors, and welding quality (shear strength of weld, weld width) was selected as response value. Accuracy of the model was verified by analysis of variance table and residual probability diagram, and interaction effect of different welding parameters combinations on welding quality was explored. The results showed that when increasing laser power, welding speed and glass fiber content, shear strength of weld increased first and then decreased. When decreasing laser power or increasing welding speed, weld width reduced. When increasing glass fiber content, weld width increased first and then decreased. Welding speed had a greater impact on shear strength of weld, and glass fiber content had a greater impact on weld width. Optimal welding parameters of glass fiber composites were determined with goal of optimal welding quality and minimum welding cost, respectively.