Studies on the laser plastic transmission welding have rrninly focused on the optical properties of material, because its optical properties significantly affect on weldability of polymers in transmission welding. Most studies, however, pay little attention to the side of mechanical engineering. In this study, Influence of laser power and lasing time is investigated by spot laser transmission welding experiment. Additionally, Research of thermal analysis is conducted to suggest rmre realistic heat source rmdel. Apart from related researches, new heat source is proposed. It is consists of three parts. One is variation of beam radius along the passing through the transmitting part. Another is Gaussian distributed beam profile. The other is volume heating method that is consist of exponentially decreasing intensity in accordance with absorption coefficient. Thenrnl analysis is conducted with proposed heat source and previous heat source rmdels, and compared with experimental results. It is found that thermal analysis results using proposed heat source model show a good level of agreement with the experimental results.