The invention discloses a welding method for an automobile top plate, and belongs to the technical field of automobile manufacturing. An automobile top plate welding clamp is utilized in the welding method. The welding method comprises the operation steps that a, longitudinal rod locking screws are loosened, the distance between telescopic longitudinal rods is adjusted and corresponds to the width of a workpiece to be welded, and the longitudinal rod locking screws are screwed for positioning; b, each split part of the workpiece to be welded is placed between electromagnets of a workpiece clamp, and a switch button is pressed; c, transverse rod locking screws are loosened to adjust the distance between telescopic transverse rods, welded parts of the workpiece to be welded are combined and adjusted to the proper body position, and then the transverse rod locking screws are screwed for positioning; d, supporting rod locking screws are loosened, the welded parts of the end faces of the workpiece to be welded are flush, and the supporting rod locking screws are screwed for positioning; and e, a welding machine is used for welding the workpiece to be welded, and the top plate is obtained. The welding method can solve the problems that during existing automobile top plate welding, clamping reliability is low, clamping is complex, overturning cannot be achieved, and existing automobile top plate welding is not suitable for welded parts of various specifications.