Because of the inherent link delay characteristics of a modular multilevel converter (MMC) based high voltage direct current (HVDC) transmission systems, high frequency oscillations may occur. Thus a small signal MMC model incorporating link delays is established. The eigenvalue analysis method is used to analyze the high frequency oscillation modes, and the underlying mechanism of high frequency oscillations is revealed. Also, a high-frequency oscillation suppression strategy based on a second-order notch filter is proposed to ensure sufficient positive damping in the high frequency band. A comparative analysis is conducted between this strategy and suppression methods using low-pass and nonlinear filters, evaluating their effectiveness in mitigating oscillations and their impact on MMC dynamic performance and fault ride-through capability. Finally, the correctness of the theoretical analysis and the effectiveness of the suppression measures are verified by electromagnetic transient simulations using the PSCAD/EMTDC platform.