In this paper, laser transmission welding experiment was carried out with glass fiber/PBT composites. Firstly, the effects of glass fiber content, laser power, and welding velocity on welding quality were explored by the response surface methodology (RSM), and the interaction effects of glass fiber content and laser power on welding quality were found to be of least significant. Secondly, microscopic morphology observation of welding seam drawing section was implemented under the change of welding velocity and glass fiber content. It was found that when the glass fiber mass content was 10%, the glass fiber and PBT polymer were tightly wound; when the welding velocity increased from 3 mm/s to 7 mm/s, the fish scale texture of the welding seam became more and more obvious. Finally, the optimal combination of process parameters for maximum welding strength and maximum welding velocity was obtained by experimental analysis.