Abstract: In view of insufficient consideration of the online strategy optimization constraining and control measures as well as the calculating speed that cannot meet the online requirements, a control performance index calculating method for DC power emergency modulation, generator tripping, load shedding and partial resection grid islanding is developed based on the participation factors,comprehensive electrical distance, reactive power-voltage sensitivity, and security-stability margin. In addition, a two-stage clustered computing method for online optimization strategy is proposed. At each stage, according to the control performance index, all control measures are combined to form the computing task with the scheduled queue to be submitted to the clustered system for parallel computation. Firstly, the transient angle stability emergency control strategy is computed to realize coordination among emergency DC modulation, generator tripping and load shedding. Secondly, on the basis of the optimal transient angle stability control strategy, the emergency control strategy of transient voltage and frequency security and stability is computed to realize the coordination between the transient angle stability with the security and stability of transient voltage and frequency. The simulation results have verified the validity of the proposed computing method.