The invention discloses an adjustable flat-panel welding fixture and relates to the field of welding. The adjustable flat-panel welding fixture comprises a workbench, bearing plates, a guide device, apositioning device, a clamping device, a lateral clamping device, an angle adjusting device, a quick angle adjusting device, a supporting base, flat panels and the like. The guide device comprises the bearing plates and guide slide bases. The positioning device comprises the guide slide bases and positioning slide blocks. The clamping device comprises spiral lead screws, the positioning slide blocks and pressing plates. The lateral clamping device comprises spiral lead screws, fixing supports and pressing plates. The angle adjusting device comprises guide shafts, index plates, gaskets and lock nuts. The quick angle adjusting device comprises a supporting frame, a supporting shaft and a double-ear chain ring. The adjustable flat-panel welding fixture is simple in structure, easy to replaceand high in recyclability, different welding angles, different clamping positions and different degrees of clamping force during flat-panel welding experiments can be adjusted, meanwhile, the attaching performance among welding pieces is guaranteed, the adjusting mode is convenient and fast, and the mechanical tooling time can be effectively saved.