Abstract <p>This study is aimed to investigate the control of the mechanism of unsteady dielectric barrier discharge (DBD) plasma actuation in flow separation of turbine blades and vortex shedding at the trailing edge, as well as the impact of excitation frequency on the control effectiveness. For the T106A turbine blades, the large eddy simulation (LES) method was used to analyze the evolution pattern of the flow field structure under the unsteady plasma actuation. Primary flow patterns and their interactions were identified through the proper orthogonal decomposition (POD) method. The induced vortex structures generated by plasma actuation are coupled with the vortex structures at the trailing edge, which significantly weakens the intensity of vortex structures, leading to a notable improvement in the spatiotemporal structure of the flow field. Simultaneously, plasma actuation enhances the momentum of low-energy fluid, stimulates large-scale turbulent fluctuations in the flow field, and suppresses irregular small-scale turbulent fluctuations. When the excitation frequency is set at the level of 0.8, the induced flow field exhibits better coupling with the vortex structures near the trailing edge. The total pressure loss coefficient diminishes by 20.96%. As the frequency increases, the improvement on flow control effect is not obvious and the wake loss can increase slightly.</p>