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遭受大扰动故障冲击后，振荡中心落点的交流断面，是互联电网送受端相互“撕裂”趋于失去同步稳定的薄弱断面。关键支路则是薄弱断面中“撕裂”最先发生的支路。识别关键支路，并采取有针对性的控制措施，对提升互联电网输电能力和抗扰能力，具有重要意义。该文以交直流混联多支路外送系统为研究对象，通过持续恶化薄弱断面稳定水平，分析各支路受扰轨迹特征差异；在此基础上，提出了关键支路动态识别方法，并揭示薄弱断面中交流支路相继失稳机制。提出了控制措施与关键支路间有功控制灵敏度评价指标，以及基于该指标的暂态稳定控制策略。实际电网仿真结果，验证了关键支路动态识别方法和稳控策略的有效性。“,”Suffered by the large disturbance fault, the ac section with the oscillation central located is the weak link at which the interconnected ac system would be lost synchronization stability and slatted. Having minimum stability margin, the key branch in the ac weak section loses stability firstly. Identifying the key branch and taking effective measures to mitigate the impact on the key branch are of great significance for enhancing the ability to resist disturbance and the transmission capacity. In this paper, aimed at the AC-DC hybrid multi-branch sending system, and based on the disturbed trajectory difference analysis during the process that the stabilization levels continued to deteriorate, the dynamic identification method for the key branch is put forward, and the successive instability mechanism of the multi-branch system is revealed. The sensitivity indicator between control power and the power of key ac branch is defined. The control strategy for improving the stability is proposed based on the sensitivity indictor. Simulation results verify the effectiveness of identification method and the stability control strategy.