In recent years, State Grid Corporation of China has been vigorously promoting smart grid construction, and cloud computing is developing rapidly. Trend of the electric power enterprise informatization construction will be the private cloud computing, which will become the comprehensive platform of smart grid. Comparing private cloud with public cloud, this paper lists differences between them and puts forward an architecture of private cloud computing to support smart gird, expounds structure of each layer, and presents concept of private cloud computing operating system and network virtualization. It provides the theoretical reference to build the private cloud computing, thus promotes the construction of the smart grid.