The invention discloses a card box gate self-locking mechanism. The card box gate self-locking mechanism comprises a card box inner housing (1), a card box gate (3) and a card box gate spring (5). The card box gate (3) is provided with a notch (6). The card box gate (3) is provided with a shoulder (7) at the notch (6). The middle part of an unlocking sheet (2) is hinged to a riveting column arranged on the card box inner housing (1) and located in the notch (6) of the card box gate (3). A long arm end (22) and a short arm end (21) are formed on the unlocking sheet (2). An unlocking sheet tension spring (4) is connected between the short arm end (21) and the card box inner housing (1). When the card box is separated from a card issuing device, the unlocking sheet (2) resets and pushes the shoulder (7) on the card box gate (3) under the effect of the unlocking sheet tension spring (4) so as to prevent the card box gate (3) to move upwards; in the process that the card box is placing into the card issuing device, a card issuing device tongue piece firstly touch the long arm end (22) and pushes the long arm end (22) away, and the short arm end (21) is separated from the shoulder (7) after the unlocking sheet (2) is rotated around the riveting column for a certain angle. The card box gate self-locking mechanism has the advantages that the mechanism is precise and simple, the cost is low, safety and reliability are realized, and the functional idea is smoothly realized.