The invention discloses a preheating and flattening device for an aluminium strip. The preheating and flattening device comprises a rack; a transmission roller is arranged on one side of the rack; an electric heating plate is arranged on the rack; an electric heating wire is arranged on the outer surface of the electric heating plate; the electric heating plate is mounted on a lifting frame; a pair of guide pipes is arranged at the inner bottom of the rack; pneumatic rods are sleeved with the guide pipes; the ends of the pneumatic rods are mounted on one side of the bottom of the lifting frame; a temperature controller is arranged at the inner bottom of the rack and is connected with the electric heating wire through a cable; a fixing seat is arranged at the inner bottom of the rack; a limiting platform is arranged on the fixing seat; a traction roller is arranged on one side of the limiting platform and is mounted on one side of the limiting platform through a fourth mounting shaft; a top seat is arranged at the inner top of the rack; a hydraulic cylinder is arranged at the lower part of the top seat; a piston rod is arranged at the lower part of the hydraulic cylinder; and a flattening plate is arranged at the lower end of the piston rod. With the preheating and flattening device, pressurized flattening operation is performed on the aluminium strip by the aid of the flattening plate, so that the flattening operation efficiency for the aluminium strip after heating treatment is greatly improved.