The invention provides a spare power automatic switching dynamic intertripping control method, device and system. The method comprises the steps that first real-time operation data sent by a line at the same level are received, and the first real-time operation data are used for representing the overload level of an inlet wire power supply at the same level; according to the first real-time operation data, load amount which needs to be cut off is computed; and a load is selected according to the load amount, which needs to be cut off, obtained by computing, and the selected load is cut off. Accordingly, during load cutting off, the load amount which needs to be cut off is computed according to the first real-time operation data sent by the line at the same level, then, the load is selected and cut off according to the load amount, which needs to be cut off, obtained by computing, the fact that the load which needs to be cut off is computed dynamically and accurately according to practical requirements is achieved, and intellectuality is high.