Abstract: A technique of 3-point localization of weld seams with structure-light visual sensor is presented. With this technique, arc welding robots can cope with the location variation of weld seams each time in batched manufacturing. On the base of suitable mathematical discription, the localization problem is transformed into determining a displacement transformation matrix. The solving process of 3-point localization method with good reliability in theory is given. Structure-light visual sensor is used to get postition information of weld seams, and precise localization of weld seams is realized quickly.