The invention discloses a spare power automatic switching and load shedding coordinated control system and coordinated control method in the technical field of relay protection of a transformer station power system. The spare power automatic switching and load shedding coordinated control system comprises a conventional spare power automatic switching module, an inter-station communication module and a remote spare power automatic switching module, which are connected sequentially, wherein the conventional spare power automatic switching module serves as a basis, and the inter-station communication module realizes a remote spare power automatic switching and allows the spare power automatic switching satisfy capacity restriction by transmitting remote spare power automatic switching starting signals and load information without causing loads. When spare capacity is insufficient, load shedding is conducted in a station to complete remote spare power automatic switching and restore optimal loads. The reliability of power supply is improved, constraints of loads and spare capacity are taken into consideration, and load may not be caused during a spare power automatic switching process. Escalation of faults may be prevented. Load shedding is combined with spare power automatic switching to maximize restored loads.