Laser transmission joining process has potential prospects in industry and medical areas because of its speed, precision, flexibility and strong environmental adaptability. Polycarbonate sheets are joined using laser transmission joining technology with Compact130/140 laser diode of Dilas. The joining process is optimized in response surface methodology. The interaction effect of key parameters including laser power, scanning speed, clamp pressure, scanning number on joint quality is researched. The results show that the interaction of laser power and scanning speed is relatively large. Increasing laser power, reducing scanning speed, increasing the mold clamping force and the scanning number can be helpful to the joint quality. The morphology of the joining area is observed with an optical microscope. Based on this research, process parameters of laser transmission joining of polycarbonate are obtained.