A complex and large AC-DC hybrid power grid has been built by China Southern Power Grid, which characterized by long distance, large capacity, AC-DC interconnected, and strong DC with weak AC. The problem of security and stability of power grid is becoming more and more serious, so it is necessary to build a large-scale power stability control system to ensure the safe and stable operation of the power grid. However, the existing power stability control system has the shortcomings of simple communication architecture, transparent communication protocol, low dependability and security, and weak anti-interference capability. Therefore, it cannot meet the requirements of high dependability and security in power stability control system for AC-DC hybrid power grid. In this paper, new technologies of communication frame recoding, unique authentication of communication identification code and verification of cyclic increasing counter are presented, which improve the reliability of communication between stations in power stability control system. A self-inspection technology based on online monitoring command is also presented, which effectively detects the hidden defects of large-scale stability control system and greatly improves the overall reliability of the whole system communication. Finally, a data encryption standard (DES) encryption algorithm is applied to encrypt interactive data between stations to ensure the communication security of the power stability control system. Experimental verification and field application show that the proposed new technologies significantly improve the reliability and security of the power stability control system.