A master/slave control system of an AC/DC power supply includes a master device. The master device is able to supply AC and DC power. The master device is connected with a plurality of slave devices through a plurality of local area network transmission interfaces. The slave devices are able to supply AC and DC power. Through the local area network transmission interfaces, a control signal can be transmitted fast for the mater device and slave devices to carry out a master/slave control. The signal transmission efficiency of the master/slave control can be enhanced greatly, so that the master/slave control is more fast and prompt. The present invention avoids the arrangement of the traditional series data communication interface and the controller area network, and simplifies the configuration and wiring of the master device and the slave devices.