This paper mainly studied the double-sided arc backing welding process of central groove,the weldability tests have been done by using dissimilar steel,semi-mechanization method and automatic method were studied both. Designed different gap width and root face height,the microstructure of the test joints and their mechanical properties are studied by means of the optical microscopy（OM）,the mechanical properties measuring equipments. The results show that the gap width is2～3 mm and the root face height is 0～2 mm,which is the best parameter for the implementation of semi-automatic and automatic MAG double-sided arc backing welding process,and the excellent welding joint can be obtained.