The invention relates to a special welding machine for multi-position welding, comprising a control platform, a base and a gas shielded welding machine, wherein one end of the base is provided with a gas bottle frame, and the other end of the base is provided with a stroke switch; the upper part of the base is provided with sliding rails; a working platform is arranged on the sliding rails; the control platform, positioning devices and a stepless speed-changing motor are arranged outside the base; the middle of the base is provided with a portal frame which is provided with the gas shielded welding machine and a welding gun fixing frame; and the base is internally provided with a speed reducing machine, a base chain wheel and a base gear. The special welding machine has the advantages that (1) linear welding of a multistation lifting arm can be realized, the staff demand is reduced, the labor intensity is reduced and the welding sped is effectively increased; (2) four edges can be welded simultaneously in one step, the stress deformation in the welding process is avoided, and the overall tensile strength of the lifting arm is guaranteed; and (3) the whole welding process is carried out at constant speed, therefore the welding continuity is guaranteed, the welding seams of a welded product are uniform and the appearance quality is improved.