Abstract: Polycarbonate plastic was welded using laser transmission welding technology. The orthogonal experiment method was applied to investigate the influence of laser power, weld speed and carbon black content on weld strength and weld quality. The effect of linear energy on weld strength was discussed. By analyzing the microstructure of welded seam, the effect of carbon black content on weld quality was further investigated. The results show that the laser power was the primary influencing factor, followed by welding speed, and then the carbon black content. The optimum welding parameters were 40 W of laser power, 40 mm/s of welding speed and 0.1% carbon black. The welding heat input had large influence on weld quality. When the range of linear energy was 0.5~1.3 J/mm, high weld strength could be attained.