For resolving the present problems of VSC-MTDC， a coordinated control strategy for converters to take part in balancing power based on local signals is designed. For the strategy， master station（MS） adopts constant DC voltage control， main assistant station adopts local-DC-voltage-based-changing-current control（LVBC）， and subsidiary assistant station（SAS） combines LVBC and constant DC current control（CDCC）. SAS is with CDCC when MS is in normal operation. When MS is out of operation and DC voltage of SAS satisfies the demand for control conversion， SAS automatically switch over to LVBC to participate in balancing power and to stabilize DC voltage. And it returns to CDCC automatically when the cause to unbalance power is removed. The simulation results on PSCAD/EMTDC platform show that the control strategy is correct and effective.