<p>To improve the aerodynamic performance and optimize the flow field structure of H-type vertical axis wind turbines (VAWTs), a split trailing-edge double-flap structure inspired by bionic fish tail fins was proposed, while maintaining the original airfoil parameters. Using 2D and 3D computational fluid dynamics (CFD), the effects of varying flap relative lengths (<i>x</i>/<i>c</i>), upper and lower flap deflection angles, and active control strategies on aerodynamic performance (<i>C</i>_<i>p</i>) were systematically investigated. First, the power coefficient and instantaneous torque of individual blades through comparative analysis to determine the optimal <i>x</i>/<i>c</i>. Second, the influence of different upper and lower flap deflection angles on the overall torque was investigated. Finally, active control strategies were applied to explore their effects on the power coefficient and tangential force. Results showed that <i>x</i>/<i>c</i> = 0.2 provided the most significant improvement. At an upper flap deflection angle of 30°, notable performance enhancements were observed across the studied tip speed ratio (<i>TSR</i>) range. When both deflection angles were 30°, the improvement extended to a wider <i>TSR</i> range. Active control increased blade surface velocity gradients, optimized velocity distributions, and enhanced blade torque.</p>