The invention provides a cooling device and method capable of preventing a heat treatment sheet material from deformation and belongs to the technical field of metal material machining. The cooling device capable of preventing the heat treatment sheet material from deformation comprises a liquid containing bucket, a fixed extruding frame, a movable extruding frame, a plurality of pressure sensors, a hydraulic cylinder and a controller, wherein a through hole is formed in a side wall of the liquid containing bucket; a sealing ring is mounted in the through hole; the fixed extruding frame is mounted in the liquid containing bucket and comprises a fixed extruding plate and a supporting plate; the fixed extruding plate is vertically connected with the supporting plate; the movable extruding frame comprises a movable extruding plate and a push rod; the movable extruding plate is supported on the supporting plate and is aligned to the fixed extruding plate; one end of the push rod abuts against one face, far away from the fixed extruding plate, of the movable extruding plate; the other end of the push rod penetrates through the sealing ring to be connected with the hydraulic cylinder; the hydraulic cylinder is connected with the controller; and each pressure sensor is mounted on one face, far away from the movable extruding plate, of the fixed extruding plate and is connected with the controller. The device provided by the invention can guarantee that the straightness of the heat treatment sheet material and temperature of a cooling medium are in needed ranges.