Disclosed are an automatic cutting device and method for rubber powder polyphenyl granule heat retaining panels. The device comprises a cutting track, a transmission lead screw, a transmission lead screw stepping motor, a horizontally moving trolley, a transmission nut, an air cylinder, a servo motor and a disc serrated wheel, wherein the cutting track is horizontally arranged above a conveying device; two tracks which are parallel up and down are arranged on side faces of the cutting track; the transmission lead screw is arranged in the position, away from the cutting track by a certain distance, between the two tracks through lead screw bases; the transmission lead screw stepping motor is arranged at one end of the cutting track and is in shaft connection with one end of the transmission lead screw; sliding blocks corresponding to the two tracks and the transmission nut corresponding to the transmission lead screw are arranged on the side face, opposite to the cutting track, of the horizontally moving trolley; the air cylinder is arranged on the side, back on to the cutting track, of the horizontally moving trolley; a piston rod of the air cylinder moves downwards, the servo motor is fixed to the tail end of the piston rod, the disc serrated wheel is arranged on a rotating shaft of the servo motor, and the transmission lead screw is mounted aslant. The automatic cutting device and method for rubber powder polyphenyl granule heat retaining panels are high in cutting precision and free of production of wastes.