A real-time demand control system includes an analysis control module, a plurality of device management modules, and a plurality of electronic devices. The device management modules integrate electricity consumption of the electronic devices and provide the electricity consumption to the analysis control module. The analysis control module predicts whether the total electricity consumption at the next time period exceeds a contract capacity according to the present total electricity consumption. The analysis control module computes and announces reduction of electricity consumption to the device management modules when the predicted total electricity consumption is possible to exceed the contract capacity. Each device management module computes one or more state adjustment options to the analysis control module according to the reduction of electricity consumption. The analysis control module selects one or more state adjustment options to switch operation states of the electronic devices so as to reduce the total electricity consumption.