With the widespread application of flexible DC transmission technology (VSC-HVDC) in offshore wind power engineering, medium-frequency oscillation (MFO) may occur when offshore converter stations are connected to offshore wind farms, seriously endangering the safe and stable operation of the system. Therefore, a virtual admittance-based MFO suppression strategy is proposed. First, a modular state space method is used to establish a small signal model of offshore wind farm when connected to a VSC-HVDC. Then, the participation factor analysis method is used to reveal the key factors affecting the MFO, and the impact characteristics of each key factor on the MFO are analyzed. Based on this, a damping control strategy is proposed to add virtual admittance to the VSC-HVDC control system. The stable range of the controller parameters is divided based on the differential influence of the damping controller on MFO and LCL oscillations. Finally, a time-domain simulation model is built in Matlab/Simulink. The simulation results show that the proposed strategy can effectively suppress MFO and improve system stability in different system operating conditions.