The invention relates to a welding tool for a chassis frame of a maize harvesting machine, in particular to a flexible robot welding tool for the chassis frame of the maize harvesting machine. The flexible robot welding tool for the chassis frame of the maize harvesting machine is low in machining and manufacturing cost and convenient to clamp, labor intensity of workers is low, the locating precision of transverse beams and longitudinal beams of the frame can be guaranteed, welding deformation can be reduced, flexibility is good, interference cannot be generated during welding after overturn, and a front face and a back face can be welded on one tool through one-time locating. The flexible robot welding tool for the chassis frame of the maize harvesting machine has the advantages that the workers can load and unload workpieces conveniently, and labor intensity is low; the position of a frame transverse beam locating mechanism and the position of a frame longitudinal beam locating mechanism on a bearing frame can be adjusted continuously, welding of frames of different series and different types can be achieved, and flexibility is good; overturn of the tool can be achieved through a welding positioner, and robot welding is achieved; the machining and manufacturing cost is low, operation is convenient, working efficiency is improved, and needs of enterprises are met.