Abstract: A passive vision sensing system for acquiring the image of GMAW molten pool was set up and a lot of clear images were obtained.Image-processing software was used to extract characteristic information which reflects the welding quality.Gray feature and pseudo-color imagewere analyzed.Gray mean and gray standard deviation distribution were used to study the process of welding with the current and voltage wave analysis.The conclusion is that the fluctuation range of the gray mean and gray standard deviation reflects the stability of the welding process.