To improve the performance of relay protection devices, a new microcomputer relay protection platform is designed. In this platform, MPC8309 based on PowerPc architecture is the core controller of the protection unit and the communication unit which are designed respectively, and a sampling board is designed independently. Boards are interconnected with high speed ethernet interface and LVDS. The software system based on Nucleus embedded real- time operating system is designed hierarchically and modularized. Combined with a specific application case, the hardware and software design of the platform are described in detail, with the key points in the process of design and the underlying configuration. The platform with perfect function and good stability can satisfy the performance requirements for protective devices. The relay protection platform is suitable for relay protection measurement and control device of power equipment of all kinds of voltage grade, and has been successfully applied to high voltage line protection devices.