The present invention discloses an access control system. In the present invention, after installing one sensor at the door, the reception sensitivity (RSSI) is set differently according to the distance based on the door, as well as configured so that the detection area on the indoor side and the outdoor side are divided based on the door. In this way, when a person holding a security tag approaches the door direction, it is possible to efficiently manage the time and attendance of the visitor through log data recording first, and to unlock the door lock status afterwards, and to the person who is located indoors. Even if the door is close to the door, the lock state of the door is prevented from being unnecessarily released, and the ground plane of the receiver is not designed to be large enough to maintain a λ/4 distance from the indoor petting point. It is to reduce the power consumption of the access control system and improve the radiation efficiency and recognition rate while eliminating the resonant frequency adjustment task to limit.