Abstract: The qualified rate of metal bobbin weldment is greatly influenced by the surface quality of welding line, to improve the surface quality and the qualified rate of welding and keep the height difference between any two points on the weld surface within 0.1 mm, a grinding method for welding line of welded bobbin based on detection of point laser is proposed. Fix the metal bobbin weldment at a certain position, and the point laser is used to detect the both sides of the welding line on the same straight line, the theoretical line is obtained by linear fitting, then the laser detects the welding line, according to the detected data to calculate the theoretical grinding position and grinding direction. Rotate the welded bobbin until all the data in one circle is detected. Grind the welded bobbin on the belt grinding machine according to the theoretical grinding position and grinding direction at all angles, then detect and analyze the surface again, the practicability of this method is verified.