The invention discloses a vehicle and an unpowered return conversion system thereof. The unpowered return conversion system comprises a trigger switch, a main air conversion valve and a parking brake pipe conversion valve, wherein a train pipe air source is connected with a main air pipe load through the main air conversion valve; the train pipe air source is connected with a parking brake pipe through the parking brake pipe conversion valve; the trigger switch is electrically connected with the main air conversion valve and the parking brake pipe conversion valve respectively; and the conversion action of the main air conversion valve and the conversion action of the parking brake pipe conversion valve are respectively controlled through the on-off condition of the trigger switch. When the original driving mode of the vehicle is changed into an unpowered mode or a mode of being driven by a train, the trigger switch is affected and the on-off condition of the trigger switch is changed, and the main air conversion valve is controlled to communicate the main air pipe load in the vehicle with the train pipe air source, so that the pressure for a main air pipe and parking brake of the vehicle can be directly provided by a train air source through the operations, and manual operations to a conversion cock, a parking brake isolation cock and a parking brake pull ring in the prior art are not needed.