Abstract: In order to study the influence of additive on laser transmission welding thermoplastic material,the experimental scheme of laser transmission welding thermoplastic material was designed.Laser transmission welding transparent polystyrene and polyvinyl chloride was successful with this method.The welding process was analysized with orthogonal method.The shear strength was tested on the workpiece.The influence of two kinds of additive;black lacquer and clearweld on welding strengnh and appearance quality was discussed.Finally,the phenomenon of black and brown welding line,welding line heave,jointing rapture was analyzed.Experiment results showed that clearweld additive was better than black lacquer additive.