This paper briefly introduces the interface model of substation automation system of IEC61850 communication system. By expounding the key technology of digital substation samples value (SMV) transmission mechanism and the common object oriented substation events (GOOSE) model of real-time and reliability, and combining one example of the digital substation, it introduces the realizing plan of the networking spare power source automatic switching device and the implementation way of logical functions of the spare power source automatic switching device, and proposes the feasibility plan of realizing the networking spare power source automatic switching device in a digital substation.