Abstract: Arc welding robots applied in the industrial production all are the teaching and playback robots.This robot requests that the workpiece is located conformably every time in the instance of the batch quantity production,otherwise teaching is requested over againg.Also there is locating problem in arc wedling robot with off-line program system.If the workpiece is located inaccurately,arc welding robot can't finish welding along the original track made by off-line program.In the paper,the locating system for planar workpiece based on hand-eye stereo vision in arc welding robot is developed.First the inside and outside parameters of the camera and the hand-eye relation are calibrated.And then the robot is con trolled and moved to the two positions.The images are captured by the camera mounted in the end effector of the robot at the two positions.Finally the workpiece's 3D coordinates in the basal coordinate of the robot are calculated by image processing and stereo vision.Experiments show that the workpiece's locating information got by locating system is accuracy.The locating system laid the foundation of independent welding.