The technical difficulties of welding by one side of J groove welding in frame beams are analyzed. According to the results obtained by a lot of the experiments,the MAG breakdown welding method is adopted. The welding is proceeded from left to right,and the positioner is employed in order to achieve a one-time welding at the PC position. The result is that a satisfactory process of welding by one side is obtained,which is important to ensure the weld quality and improve the produce efficiency.