In order to solve the problem of cumbersome secondary equipment configuration and complex file generation in the process of new construction and transformation of smart substations, this paper proposes a plug-and-play theoretical model of secondary equipment. In order to realize the plug-and-play function, a framework for secondary devices is first designed, and for the designed framework, the required functions are realized at the hardware and software levels. In terms of hardware, a triple-core hardware platform composed of dual-core heterogeneous processors and FPGA is adopted. In terms of software, a hierarchical design is realized. It is composed of a support layer, a functional layer, and an application layer system. These accomplish the decoupling of layers and facilitate subsequent maintenance and reuse of software components. For the secondary equipment model, it adds plug-and-play unique data and a function description, and elucidates the three aspects of equipment, data and function. To test the application of functions, simulation of protection and measurement and control is carried out. Also the control and verification logic of secondary equipment sequence control, anti-error locking, five-proof locking and virtual terminal verification are designed. Finally, the functional test proves that the design model can correctly and automatically read the equipment configuration, and download and modify the configuration of related parameters. This work is supported by the Science and Technology Project of State Grid Corporation of China (No. 52130416001U).