In this paper, a diode laser was used to conduct laser transmission welding experiments on polycarbonate with aluminum film as the absorption layer. The welding process parameters were optimized by the combination of single factor experiment method and response surface method with different aluminum film width as the main influencing factor, combined with laser power and welding speed. The fitting equation and the optimal welding process parameters were obtained. The relationship between the width of the aluminum film and the width of the weld was analyzed. The finite element model based on the middle layer of aluminum film was established by COMSOL software. The temperature field distribution under the welding process parameters was studied. The results show that the simulated weld width is consistent with the experimental weld width.