High-intensity magnetic field will generate at the pipe opening after cutting the pipe which has been buried underground for a long time, causing welding unable to be executed for connecting pipes. When pipe degausser is used, i.e. winding cables along the pipe opening, a magnetic field will generate temporarily at the opening after energizing according to the electromagnetic induction principle, the direction of which is opposite to that of the pipe’s magnetic field, thus offsetting the original magnetic field and realizing the welding operation.