<p>A plane-welding flange pre-deforming mechanism includes a flange (1) and a steel tube (2). The end of the steel tube (2) is welded with the flange (1). A geometric center of the flange (1) adjacent to the welded part offsets away from the steel tube (2) before welding operation is performed. An offset part is provided to form a pre-deforming section (3). The mechanism requires less manufacturing cost and less labor.</p>
