According to the characteristics and requirements of the UHV power grid， as well as the development of modern electronic technology and communication technology， SCS-500E security and stability control system is designed. The general platform structure of hardware and software of the SCS-500E security and stability control system is introduced. Some techniques， such as， the characteristics of SCS-500E—high-speed communication based on FPGA， criterion of non-fault line tripping based on local electrical measurements and management of set-value mapped， are described. The digital and physical simulation for the national model UHV AC project with SCS-500E system is presented. The applications of the SCS-500E system on field projects are also included.