The invention relates to an access protection system of an emergency standby power supply of a battery-powered device. The system is composed of an internal main board circuit and an emergency standby power supply. The internal main board circuit is connected to the emergency standby power supply by a standby power detection and access circuit. The standby power detection and access circuit includes a relay JDQ1 connected between a positive electrode and a negative electrode of the emergency standby power supply; and a contact group switch of the relay JDQ1 is connected with the internal main board circuit and the emergency standby power supply electrically. According to the invention, the relay JDQ1 is used for controlling connection between the input terminal of the emergency standby power supply and the internal main board circuit. When the emergency standby power supply is not connected or the access polarity error of the emergency standby power supply occurs, the emergency standby power supply is disconnected with the internal main board; and when emergency standby power supply is connected correctly, the emergency standby power supply is connected with the internal main board. Therefore, reliable protection on the internal main board circuit is realized.