Abstract: The morphology of molten pool, especially the volume of molten pool can not be measured directly by the current measurement methods. In this study, surfacing welding of thick 304 stainless steel plate with high-power disk laser welding was conducted. With extra auxiliary infrared laser light and highspeed camera, clear images of the molten pools and their shadows were obtained, and then the shadow area of molten pool was extracted to be analyzed by one-dimensional linear regression equation and correlation coefficient analysis method. The experimental results confirmed that the shadow area variation of molten pool had positive correlation with welding quality, and this provided a new method for test of welding quality.