A self-cleaning device for arrangement in in a wall-mounted air conditioner, comprising: a filtering net disposed on the outside of a heat exchanger, which includes an upper filtering net and a front filtering net, and is used for absorbing the dust of air passing through the heat exchanger; a dust sweeping assembly with a detachable brush, the dust sweeping assembly being disposed on the outside of the filtering net and is used for sweeping the dust on the filtering net; a drive device with a drive motor and a transmission mechanism, which is used for driving the dust sweeping assembly to slide on the filtering net to sweep off the dust; a dust box which is used for collecting the dust and is detachably disposed in the air conditioner to clear out the dust in the dust box; a dust exchanging device which is disposed on the left or right side of the filtering net, and is used for transferring the dust swept out by the dust sweeping assembly into the dust box, characterized in that, the dust exchanging device is a rectangle frame, in which a brush roll for absorbing the dust is pin-jointed in parallel with a side edge of the filtering net, the brush roll is one of a circular cylinder, semi-cylinder and elliptical column, a reset mechanism set on the brush roll is made of a spring or a tension spring, the dust exchanging device is respectively located in slots set on the left or right side of the upper filtering net and front filtering net, and there is a communicated dust passage with downward inclination in the bottom of the slots, a dust box slot whose interior is communicated with one of the slots is located under the slot set on the side of the front filtering net, the dust box is a box structure with a opening that is communicated with the bottom of the slot is pull-pluggably located in the dust box slot; blocks are pin-jointed at both ends of the brush roll, the blocks freely rotate in the reverse direction of the filtering net and impulse the brush roll to synchronously rotate to in the direction of the filtering net, the blocks have a first reset mechanism, and in a reset state the blocks are oriented in the direction of a hatch of the frame; an inward extended baffle with a second reset mechanism which is parallel with the brush roll is pin-jointed on the inner side of the frame of the dust exchanging device near the filtering net, felt is set on the baffle's side near the brush roll to realize a second dust exchanging, and a soft baffle is aslant set along the tangent outwards on the other side of the brush roll, and is deflected away from the filtering net. a filtering net disposed on the outside of a heat exchanger, which includes an upper filtering net and a front filtering net, and is used for absorbing the dust of air passing through the heat exchanger; a dust sweeping assembly with a detachable brush, the dust sweeping assembly being disposed on the outside of the filtering net and is used for sweeping the dust on the filtering net; a drive device with a drive motor and a transmission mechanism, which is used for driving the dust sweeping assembly to slide on the filtering net to sweep off the dust; a dust box which is used for collecting the dust and is detachably disposed in the air conditioner to clear out the dust in the dust box; a dust exchanging device which is disposed on the left or right side of the filtering net, and is used for transferring the dust swept out by the dust sweeping assembly into the dust box, characterized in that, the dust exchanging device is a rectangle frame, in which a brush roll for absorbing the dust is pin-jointed in parallel with a side edge of the filtering net, the brush roll is one of a circular cylinder, semi-cylinder and elliptical column, a reset mechanism set on the brush roll is made of a spring or a tension spring, the dust exchanging device is respectively located in slots set on the left or right side of the upper filtering net and front filtering net, and there is a communicated dust passage with downward inclination in the bottom of the slots, a dust box slot whose interior is communicated with one of the slots is located under the slot set on the side of the front filtering net, the dust box is a box structure with a opening that is communicated with the bottom of the slot is pull-pluggably located in the dust box slot; blocks are pin-jointed at both ends of the brush roll, the blocks freely rotate in the reverse direction of the filtering net and impulse the brush roll to synchronously rotate to in the direction of the filtering net, the blocks have a first reset mechanism, and in a reset state the blocks are oriented in the direction of a hatch of the frame; the dust box is a box structure with a opening that is communicated with the bottom of the slot is pull-pluggably located in the dust box slot; blocks are pin-jointed at both ends of the brush roll, the blocks freely rotate in the reverse direction of the filtering net and impulse the brush roll to synchronously rotate to in the direction of the filtering net, the blocks have a first reset mechanism, and in a reset state the blocks are oriented in the direction of a hatch of the frame; an inward extended baffle with a second reset mechanism which is parallel with the brush roll is pin-jointed on the inner side of the frame of the dust exchanging device near the filtering net, felt is set on the baffle's side near the brush roll to realize a second dust exchanging, and a soft baffle is aslant set along the tangent outwards on the other side of the brush roll, and is deflected away from the filtering net.