In the transition period of UHV power grid construction, AC-DC interaction intensifies, the sending end and the receiving end tightly coupled, security and stability operation of power grids rely more on the Security and Stability Control System (SSCS), which show a large-scale, wide area and complicated trend in recent years, therefore the research and design on reliability of SSCS is particularly urgent. Based on the analysis of the composing principle and working mode of SSCS, the characteristics and difficulties of the reliability research are extracted, and the main factors that influence the overall reliability of SSCS are point out. In view of current research on SSCS reliability not enough systemic, and failure to grasp the key link, the key ideas of the reliability research are put forward from equipment tripping criterion, control mode, communication channel, operation mode, architecture and other aspects, thus forming the overall framework of the reliability research of SSCS, which has an important guiding significance for reliability optimization design of SSCS as well as the power grid secondary system. This work is supported by Science and Technology Project of State Grid Corporation of China “Research on Top-level Design of UHV AC/DC System Protection”.