For the common problem of the controller order is too high when using the robust control method to design damping controller for HVDC transmission system. A method based on static H∞ loop shaping is proposed to suppress the sub-synchronous oscillation and low frequency oscillation. The designed controller has the same order as the weight function. The order-reduced model and the sub-synchronous oscillation and low frequency oscillation modals in AC-DC system are obtained by total least squares-estimation on signal parameters via rotational invariance techniques. Then, the different oscillation frequencies are decomposed into different channels by Butterworth band-pass filters. The additional robust damping controller is designed based on static H∞ loop shaping, restraining the interaction between control channels. Xiangjiaba-Shanghai DC link under island operation condition is simulated using electromagnetic transient program PSCAD/EMTDC to demonstrate the proposed control strategy. Simulation results in PSCAD/EMTDC show that the designed multi-channel damping controller can well suppress different oscillation modes of the system and possesses good robustness. Besides, the order of the controller is low and it adopts output feedback control, which are convenient for practical application. This work is supported by Science and Technology Project of State Grid Corporation of China (No. SGNXDK00 BGJS160021).