Abstract: hen the power system operates under non-ideal conditions, significant voltage fluctuations occur. The utilizatuion of a passivity-based control strategy in the shunt active power filter (SAPF) may not effectively and accurately regulate power quality . Besides, conventional sliding mode control is also prone to buffeting. In the light of this, a passive super-twisting second-order sliding mode control strategy is proposed in this paper, which is a combination of passivity-based control and super-twisting second-order sliding mode control with stronger resisting disturbance capacity. First of all, the Euler-Lagrange model is established based on positive and negative sequence separation, in accordance with the mathematical model of active power filter. Secondly, the passivity of model is analyzed, and a passivity-based controller is designed according to its passiveness. Meanwhile, the passivity-based controller is further optimized by using the super-twisting second-order sliding mode control, thereby enhancing the robustness and capacity of resisting disturbance. Finally, simulation experiments are carried out under both ideal condition and four non-ideal conditions, namely load mutation, load imbalance, grid voltage imbalance and single-phase voltage mutation. The simulation results verify the effectiveness and superiority of the passive super-twisting second-order sliding mode control strategy.