The influence of laser transmission welding parameters for polypropylene (PP) plastics on welding quality is investigated by orthogonal design method. Tensile and section tests are conducted for experimental samples, and the influence of welding factors on tensile strength and welding seam size is analyzed, which indicates subsequence of the influence of welding parmeters on PP plastics is welding velocity→laser frequency→cooling time→fixture pressure→beam diameter on the material→laser power. And high laser power density can cause resulting from coking on samples′ faces black welding line and fake fracture appears when welding seam is not even. The optimized welding parameters are determined by using range method.