Abstract: According to the study on linear track and global distribution of plasma size signals in laser welding, it is found that the global signals distribution feature of plasma has a close relationship with the real laser welding conditions. As aresults anew method based on integral analysis for plasma size signals and its transform feature model has been established in this paper. The results show that this method can not only effectly remove the random noise signals and the negative influence of the signals fluctuation during data treating process, but also has special features on its repeatability and legibility. Therefore, it is a quick and accurate way in testing the change of plasma morphology in laser welding.