A device for detecting the flatness of a sheet material includes a conveyor, a gantry, a beam, an industrial camera unit, a speed measurement unit, a vibration measurement unit, a multi-line laser, a cable carrier, an industrial controller, and a control cabinet. The conveyor is disposed beneath the gantry and includes a plurality of pinch roll assemblies for feeding a sheet material. The beam is disposed on the gantry and includes a first side and a second side. The industrial camera unit is disposed on the first side of the beam and includes at least two industrial cameras. The speed measurement unit is disposed between the at least two industrial cameras. The vibration measurement unit is disposed on the second side of the beam and includes at least two distance measurement devices. The multi-line laser is disposed between the at least two distance measurement devices.