Cascading failure mode and evolution process is much more complex and changeable because of the much coupling between the renewable generation and the AC/DC power system after system disturbance. Further research of the risk assessment and control strategy of this kind of cascading failure is required. Firstly, in order to fully consider the interaction between the practical control and protection devices action and system electrical quantities, time domain simulation method based on evaluation index of security devices such as relay devices is used to search fault chains with high risk. Secondly, a new emergency control method based on fault chain information is proposed, to set up emergency control measures for single disturbance that can evolve into cascading fault chains but without emergency control measures. This new control method can further strengthen and perfect the ability to block the fault chain of cascading failure of current emergency control system. Aiming at minimizing the total risk cost of control, the coordination and optimization of preventive control and emergency control are carried out, and the coordinated control optimization model and implementation program are given respectively. Finally, simulation results and analysis based on real-sized power grid in Northwest China prove the rationality and effectiveness of the proposed control method. This work is supported by Science and Technology Project of State Grid Corporation of China (No. 5229NX16001D) “Study on the Practical Prevention and Control Strategy of Cascading Failures of Ningxia Sending end Power Grid with Multi-HVDC and High Proportion of Renewable Energy”.