Abstract: The current operation mode and requirements of the bay-group control unit in the smart substation are analyzed,and the design principle and concept of bay-group control units are introduced.By analyzing the network data flow of the process level,the details of the hardware and software design and key technologies are described.Then this paper proposes the architecture and two kinds of operation modes of the measurement and control system based on bay-group control units in smart substation.The implementation of information and control in these two modes is also described.The feasibility of the design scheme is verified by building the experimental environment.