The invention discloses a conveying chain with the adjustable width and a forming machine thereof, wherein the forming machine comprises a plate material heating part, a plate material forming part and a width-adjustable conveying chain; the width-adjustable conveying chain comprises a power device, a synchronizing device, two chains, two chain frames and three width adjusting mechanisms arranged at the starting end, the middle section and the tail end; the chain frames are arranged on the three width adjusting mechanisms; chain gears are arranged on the width adjusting mechanisms arranged at the starting end and the tail end; the two ends of the chains are respectively erected on the chain gears of the width adjusting mechanisms arranged at the starting end and the tail end, and the middle of the chains is supported by the chain frames; the two chain frames are symmetrical and are respectively arranged at one side; each width adjusting mechanism comprises two adjusting frames, a lead screw and an adjusting motor, and the gap adjustment of the chains is realized through the matching between a screw sleeve and the lead screw on the adjusting frames; the power device is connected with the chain gear of the starting end adjusting mechanism through the synchronizing device; the synchronizing device comprises a transmission gap adapting mechanism.