Welding clamping fixture for midpiece of monocoque bus frame

The invention relates to a welding clamping fixture for a midpiece of a monocoque bus frame. The welding clamping fixture comprises an underframe on which two guide rails are arranged in parallel, wherein at least two longitudinal beam positioning devices perpendicular to the guide rails are arranged on the guide rails, each longitudinal beam positioning device comprises a bracket, slider blocks which are matched with the guide rails in a guiding manner along the length direction of the guide rails are arranged at the bottoms of the brackets, a longitudinal beam clamping seat is arranged at the top of each bracket, and a diagonal-bracing clamping seat is arranged between the two longitudinal beam clamping seats; and traverse beam positioning devices are arranged at outer sides of the both ends of each longitudinal beam positioning device on the underframe, and each traverse beam positioning device comprises an adapting pole on which a traverse beam clamping seat is arranged. When the welding clamping fixture