Network Control Systems Security - Plaintext transmission is the major way of communication in the existing security and stability control (SSC) system of power grid. Such type of communication is easy to be invaded, camouflaged and hijacked by a third party, leading to a serious threat to the safe and stable operation of power system. Focusing on the communication security in SSC system, the authors use asymmetric encryption algorithm to encrypt communication messages, to generate random numbers through random noise of electrical quantities, and then use them to generate key pairs needed for encryption, at the same time put forward a set of key management mechanism for engineering application. In addition, the field engineering test is performed to verify that the proposed encryption method and management mechanism can effectively improve the communication in SSC system while ensuring the high-speed and reliable communication.