In this article, a second-order sliding-mode control (SOSMC) based on supertwisting controller for LC-coupling hybrid active power filter (LC-HAPF) is proposed. Among the literatures review studies, hysteresis-based current controller, which is a special implementation of sliding-mode control, is usually used due to its simplicity, robustness, and good dynamic performance for reference tracking. However, it generates a nonfixed switching frequency for the power filter, which leads to undesirable harmonics problem. The proposed SOSMC ensures the good robustness and dynamic performance of using the conventional sliding mode control with an improved steady-state performance and disturbance rejection capability. In addition, with the help of supertwisting controller, the proposed SOSMC can achieve fixed switching frequency characteristic. First, the control objective and the design methodology of sliding surface are discussed and given in this article. Second, a detailed parameter design procedure under stability, system parameter variation, distorted grid voltage, and grid frequency variation consideration is provided. Then, experimental results on a three-phase four-wire LC-HAPF are carried out to verify the steady-state and dynamic performances of the proposed SOSMC compared with other representative current controllers. Finally, the disturbance rejection capability under different grid conditions of the proposed SOSMC is also verified by experimental results.