The design characteristics of instrumentation and control (I&C) system in nuclear power plants (NPP) is that the design cycle is long, the data correlation is complex, and there are many interfaces. Traditional I&C design mainly for using design tools in design process. The design data is not connected and the results are presented in the form of documents. The data correlation relationship cannot be reflected in the design documents. When design input information changes, its impact range cannot be directly obtained, and often depends on the experience of the design personnel for judgment, resulting in inconsistency of design data. In order to solve the above problems, this article summarizes and organizes the design process, then connects the entire design cycle data link of the I&C system, and establishes data correlation. Based on this, this article establishes a hierarchical management method for I&C system data management, and builds a digital design platform for I &C system. At present, the platform has been applied in the design of I&C systems for nuclear power plant at China National Nuclear Power design units. The platform has been recognized by designers and project managers, and can meet the design requirements of instrumentation and control systems, while ensuring the integrity and consistency of design data. It can provide design ideas for digital design of other platforms.