A canvas cover launching device to prevent crimps on the canvas and achieve flattening effect on the canvas, having a frame and a mounting rack on one side, a hydraulic control valve operated by control levers is on the mounting rack. Two driving plastic rollers and a surface smoothening plastic roller are rotatably connected to the frame from inside to outside of the frame sequentially; corresponding ends of the two driving plastic rollers on a same side are connected to a transmission component enabling the two driving plastic rollers to rotate towards the same direction. A synchronous transmission gearbox is provided to connect corresponding ends on a same side of the surface smoothening plastic roller and one of the two driving plastic rollers more proximal to the surface smoothening plastic roller. Hooked plates are symmetrically provided on two ends of the surface smoothening plastic roller respectively.