The invention belongs to the technical field of bridge cover plate production, and particularly discloses a bridge cover plate flanging device and a bridge cover plate machining method. The bridge cover plate flanging device comprises a workbench, stand bars and a motor; a first bearing and a second bearing are symmetrically embedded in the left side and the right side of a workbench body, third bearings are uniformly and longitudinally embedded in the right side of the workbench body, and fourth bearings are uniformly and longitudinally embedded in the left side of the workbench body; the outer wall of the first rotary shaft and the outer wall of the second rotary shaft are sleeved with rotary rollers; a right-angle supporting plate is welded to the right side of the top of the workbench;and a spiral baffle is welded to the left end of the right-angle supporting plate. A machining method of the bridge cover plate flanging device comprises the specific following steps that S1, a coverplate is put between the two rotary rollers to be clamped, and S2, the device is started so that the cover plate can move backwards at the constant speed, the cover plate is limited by the spiral baffle, and accordingly, flanging is conducted on the cover plate. Through the scheme, the machining steps are simplified, and the machining efficiency and the product percent of pass are improved.