For single-phase DC-AC power conversion, power decoupling is always required due to the existence of double-line-frequency ripple caused by the instantaneous unbalanced power between AC and DC side. The typical power decoupling method utilizes a large electrolytic capacitor and consequently increases the passive components requirement. The active power decoupling scheme introduces an additional low power converter to compensate the ripple, which inevitably increases the system cost and control complexity. To overcome these drawbacks, this paper proposes a novel suppression method based on three-level topology. By optimizing the capacitance design and improved control algorithm, the instantaneous unbalanced power is dynamically redistributed between two series connected intermediate capacitors in order to make the capacitor voltage ripple complementary to each other. Thus the de-link voltage ripple can be reduced to a large extent. Simulation verifies the correctness and effectiveness of the new suppression method.