Abstract: Automatic narrow-gap arc welding can be used in rail welding.By oscillating and moving the bacilliform welding torch,it can join together the rails by fusing two side walls of groove.While,the swinging torch control is open-loop control,which can lead to the accumulated swing error.In order to decrease the error,a double CCD visual sensor system was used to observe the welding pool for the existing equipments and rail seam arc welding techniques.And then it calculates the position offset and oscillating angle offset of the welding wire can be calculated in real time to control the torch movement.The results show that the proposed method can effectively reduce both the position offset and the oscillating angle offset,and avoid welding defect.