The invention provides an automatic purging device for a rail transit vehicle. The automatic purging device is composed of a fixed base, supporting plates, a guide base, a driving rod, a guide rod, a connecting rod, a vertical plate, a lateral purging pipe, a horizontal electric push-pull rod, a vertical electric push-pull rod, nozzles and the like. The fixed base is installed on the side wall in a room or a fixed support. A base plate, the fixed base and the supporting plates are of an integrated structure. The guide base is driven by the horizontal electric push-pull rod to slide forwards and backwards along the guide rod so as to adjust the horizontal travel and is driven by the vertical electric push-pull rod to slide up and down along the driving rod and the connecting rod to adjust the vertical travel, so that the nozzles are adjusted to the optimal purging position, and the purging effect is guaranteed. The automatic purging device is reasonable in structure design, the purging quality is high, and the labor efficiency is effectively improved.