交流跨区长距离弱联络线是电网同步稳定运行的薄弱环节。以华北-华中特高压交流互联电网为对象，研究大扰动冲击后系统振荡中心落于长治-南阳特高压交流联络线时，主要电气量受扰轨迹特征；揭示互联电网稳定裕度较小时，联络线有功功率轨迹出现“双峰”波动机理；识别峰值时刻对应的跨区互联电网同步稳定裕度及各电气量综合特征；在此基础上，定义紧急功率控制启动判据以及退出判据；提出利用多直流紧急功率控制改善互联电网稳定性的策略。特高压互联大电网的仿真结果，验证了控制判据及策略对降低互联电网解列风险的有效性。“,”Trans-regional long-distance tie-line is the weak link that threatens the transient rotor angle stability of power system. The UHVAC tie-line connecting North China Power Grid (NCPG) with Central China Power Grid (CCPG) was taken as a case, the transient trajectories characteristic for tieline under short-circuit fault conditions were studied. It was revealed that active power disturbed trajectory has the mechanism of two peaks when stability margin of interconnected gird is small. Based on the relationship between disturbed trajectory characteristic and stability margin, the active power emergency control start criterion and revocation criterion were defined. The active power emergency control strategy for Central China Power Grid multi-HVDC system was presented. Simulation results verified that the stability of UHVAC interconnected system can be significantly improved by using the proposed emergency control criterion and strategies.