Abstract: A weld position measuring model based on the weld pool image centroid was studied.During the welding process the weld pool images were acquired by a vision sensor.The fore region of the weld pool was chosen as a processed image area which was processed by the median filter and image gray transformation. Also, the image centroid coordinates corresponding to this processed image area and the seam deviations between the torch and weld could be obtained.Several groups of the weld pool images and the experiment as data including the image centroids and seam deviations were collected in different welding conditions.Then the relationship between the weld pool centroids and the seam deviations was researched by using of the least square regression arithmetic, and the mathematical equations for calculating the weld position by the weld pool centroid were deduced.Finally, by analyzing these mathematical equations a common model was established for measuring the weld position based on the weld pool centroid.The computer simulation and real experiment results showed that the weld position could be effectively detected by this measuring model.