Digitization is the essential feature of a new round of informatization. The rapid development of digital technology has promoted the leap of social informatization, and promoted the wide application of information machines composed of computers and networks in the field of power grid. This paper creatively puts forward the π model theory for analyzing social information processing. On the basis, the theoretical model of digital power grid is analyzed. The four main characteristics of digital power grid are extracted, and the overall architecture of digital power grid is constructed based on physical system, information system and business system, which lays a solid foundation for the research and development of digital grid.