Abstract: In order to ensure the network security of China's high-speed railway signal system, the network security issues including the central traffic control (CTC) system, train control system, centralized signal monitoring system and the GSM-R system were analyzed generally. Subsequently a unified network security control and management strategy was proposed based on the software-defined networking (SDN) architecture. The centralized management and unified security policies are achieved in one physical network, and the original control logics between sub-networks including CTC network, train control network and centralized signal monitoring network are all software-defined in the control plane, which enables the finer and unified control of the whole network. Using the logically centralized controller, the unified device register control, communication control and packet traceability are all achieved, thus improving the network security and reducing the management complexity. According to the analysis, the proposed architecture is centrally managed, network programmable and unified of the security policy. The proposed strategy is better than the distributed control network for the management of China's high-speed railway signal system network security and can solve the complex management of networks' interconnection of different security levels.