Abstract: Based on the lifting mechanism of Gurney flap（GF）applied at isolated airfoil trailing edge,an active GF is installed on straight blades of a vertical axis wind turbine（VAWT）. It actively adjusts the flap height with the rotation of VAWT blades. It extendes the blade surface when the blade is in the upstream area and retreats the blades surface in the downstream area to increase VAWT power coefficient. Two-dimensional CFD simulation is carried out to study turbine performance at different tip speed ratios. The control strategy of active GF is proposed. Numerical results reveal that the VAWT power coefficients mounted with active GFs are higher than that of the original VAWT over all tip-speed ratios. The relative increase of power coefficient is 5.14% under the operation condition of maximum power coefficient（λ=1.75）. Proper orthogonal decomposition（POD）is used to analyze the coherent vortex structure in the turbine wake. Small turbulent structures over 5 thorder modes is the main reasons of the energy losses. Active GF limits the vortex strength of the5 thorder structures during the blade rotation and reduces the flow losses in the wind energy capture and transition.