Abstract: When an asynchronous interconnected power grid is formed with the sending power grid connected to the receiving end only by a series of HV/UHV DC or flexible DC lines, large capacity DC blocking will occur, which will lead to frequency and voltage problems in the sending and receiving end. In this paper, for the multi-DC island system after asynchronous interconnecting network, a coordinated control strategy for power support under DC blocking emergency fault is proposed based on the fastness and controllability of DC system. Firstly, the active power allocation algorithm is proposed considering the voltage level at the receiving end by analyzing the influence of the strength of AC power grid and the power flow transfer. Secondly, through the coordination of such different control measures as DC power RUN UP/RUN BACK, FLC, cutting machine by the stabilization control device and sub-round cutting machine, a coordinated control strategy of multi-DC islanded systems is proposed. Finally, a set of coordinated control system is built, and the effectiveness of the system is verified through the RTDS simulation of the South China Power Grid in summer 2016.