The invention relates to a device for treating automobile exhaust with an air plasma. The device comprises a high-voltage direct-current power supply and two insulating plates, wherein the two insulating plates are disposed oppositely; one insulating plate is provided with at least one exhaust inlet; the other insulating plate is provided with at least one exhaust outlet; a grounding electrode and a plurality of conductive tubes are disposed between the two insulating plates; the grounding electrode is connected with a grounding end of the high-voltage direct-current power supply; the plurality of conductive tubes are connected with a high-voltage end of the high-voltage direct-current power supply; the plurality of conductive tubes are annularly distributed; and each conductive tube is provided with a plurality of steel needles along the length direction. The invention also relates to a method for treating the automobile exhaust with the air plasma. According to the device and the method, a large treatment space can be obtained, the device can be rapidly mounted on an exhaust pipe of an automobile, the automobile exhaust is treated conveniently at any time in any place, the vehicle-mounted effect can be realized, the automobile exhaust is efficiently decomposed and the treatment energy consumption is low.