The invention discloses a safe self-locking/unlocking device and an automatic vehicle outer slippage door system. The automatic vehicle outer slippage door system comprises a slippage door body, a guide rail, a power mechanism, the safe self-locking/unlocking device, a transmission mechanism, a connecting mechanism and the like. The safe self-locking/unlocking device is exquisite in structure andreliable in transmission, can realize power transmission under the normal working condition and can cut off power transmission and remove reverse containment in the case of a failure. According to theautomatic vehicle outer slippage door system, a driving wheel is connected with the output shaft of a motor through the safe self-locking/unlocking device; the driving wheel and a driven wheel drivea closed transmission chain between the driving wheel and the driven wheel to rotate, so that automatic opening and closing of the outer slippage door body can be realized under the normal working condition; and in the case of a failure, the outer slippage door body can be manually opened through external force without adopting any clutch.