The tidal current turbine was paid more and more attentions, a flap control strategy is proposed for the hydrodynamic problem of its impeller airfoil, the hydrodynamic dynamic characteristics of the turbine with different flap airfoil are calculated, the variation law of the torque coefficient of the vertical axis tidal current before and after the flap control was analyzed. The results showed that the proposed control strategy can effectively reduce the amplitude of the torque coefficient without affecting the mean value of the moment coefficient, while the amplitude coefficient of the asymmetric flap wing was smaller than that of the symmetrical flap; by analyzing the flow field structure, it was found that the flow field of the trapezoidal trailing edge of the control strategy was more slender than the flow field without the control strategy; the flap controled the vane after the blade is turned into the rotation trajectory, which had little effect on the downstream flow field and is easy to dissipate; the azimuth angle of the large vortex was 160°~260°, and the vortex intensity increased, the phenomenon was improved after the control strategy was applied.