Flexible DC transmission technology based on modular multilevel converter has gradually become the best grid connection scheme for large wind farms, and the system has the risk of broadband oscillation. In order to suppress this kind of oscillation, this paper calculates the dominant oscillation mode of the system based on eigenvalue analysis method, and further quantitatively analyzes the dynamic influence of various parameters of the system on the oscillation instability modes. It is concluded that the damping ratio of the system can be effectively improved by adjusting the control parameters of the grid-side converter of the wind farm, and a control parameter optimization algorithm of the grid-side converter of the wind farm based on eigenvalue sensitivity is proposed. In order to further reduce the oscillation risk of the system and make the system adapt to various operation conditions, a virtual resistance is added between the wind farm and the DC converter station, and an additional damping controller of the DC converter station sending-end converter based on the virtual resistance is designed. The time domain simulation model of the system is built based on PSCAD / EMTDC. The simulation results show that the compound oscillation suppression method combining the control parameters optimization of grid-side converter and the additional damping controller based on virtual resistor has better damping effect.