With the continuous development of the wind power industry, the scenarios of direct drive wind farms being transmitted through LCC-HVDC transmission systems are increasing. However, the problem of sub/super synchronous oscillation cannot be ignored. In response to the stability issues that may arise when wind farms are connected to the LCC-HVDC grid, an admittance model of the LCC-HVDC system considering commutation angle was established. Based on impedance analysis, the sub/super synchronous oscillation problem of the system in the scenario of direct drive wind farm connection was studied, and the reasons for the oscillation were verified through time-domain simulation. An additional damping control strategy was proposed by combining impedance analysis and time-domain simulation, and the effectiveness of the suppression strategy was verified. The research results indicate that adopting oscillation suppression control strategy can significantly improve the stability of the system.