The invention relates to a switch cabinet and a pressure relief device thereof. The pressure relief device of the switch cabinet comprises an installation frame, which is fixed at the top of a cabinetbody of the switch cabinet. The switch cabinet pressure relief device further comprises a top plate and two trapezoidal sealing plates. The top plate has a cross beam part for forming a cross beam. The upper bottoms of the two sealing plates are connected through the cross beam part; the lower bottoms of the two sealing plates are fixed to front and back side plates of the installation frame respectively; and two pressure relief openings are formed in the left side and the right side of the cross beam part. Pressure relief cover plates used for blocking the pressure relief openings are hingedto the left side and the right side of the cross beam part respectively, and when the pressure relief cover plates are pushed open by high-temperature and high-pressure gas during closing-opening fault current of a circuit breaker to realize pressure relief; the two sealing plates, the cross beam part and the two pressure relief cover plates form a roof structure with a pitched roof before the pressure relief cover plates are opened, wherein the pressure relief cover plates form the roof surface of the roof, the cross beam part forms the ridge of the roof, and the sealing plates form a roof truss of the roof; and the high-temperature and high-pressure gas can push open the pressure relief cover plates on the top and can be quickly discharged out of the cabinet body.