Abstract: A method is proposed for selecting the modulation signals of multiple HVDC supplementary controllers. The dynamic characteristic of system is considered in effective relative gain array (ERGA) that utilizes the information of bandwidth and steady gain, which can effectively reduce the interaction of multiple HVDC and avoid mode resonance to facilitate the design of decentralized control. At the same time, a coordinated decentralized control strategy of multiple HVDC is presented based on ERGA. Firstly, the system transfer function of different desirable signals is identified through the TLS-ESPRIT algorithm, the system oscillation mode and vibration mode are analyzed, and the steady-state gain and band width of each feedback signal are obtained. Secondly, the interaction influence degree of different paired signals is analyzed quantitatively based on ERGA, and the best paired signals with the minimum interaction are selected. In the end, the damping controller is designed by considering time lagging. The simulation results obtained with the EMTDC/PSCAD tool verify the efficiency of proposed strategy.