Abstract: A state of charge (SOC) equalization control strategy based on adaptive second-order filtering is proposed for energy storage power stations to mitigate wind power fluctuations. First, to address the time-series phase lag issue in traditional filtering algorithms, a suppression model and a parameter design method are proposed based on the second-order filter. The discrete time-domain model is derived using the bilinear transformation. On this basis, an adaptive control method for the filter constant based on grid-connected constraints is proposed, which takes into account wind power stabilization and energy storage power distribution. In this manner, the power demand and operational burden of the energy storage stabilization process can be reduced. Subsequently, to address the SOC inconsistencies existing in the power tracking process of energy storage units within the energy storage system, an average weighted control algorithm is adopted to achieve online SOC balancing. Meanwhile, considering the varying aging levels of energy storage units, a quantitative evaluation method for energy storage aging is proposed based on rain-flow counting to screen aging energy storage systems. An SOC balancing control method is proposed for the process of replacing old energy storage devices, to ensure the secure and stable operation of energy storage power systems during flat cycles. Finally, actual power data are employed to validate the effectiveness of the proposed strategy.