Abstract: A wing-in-ground-effect (WIG) vehicle is a special type of aircraft that utilizes the "ground effect" to fly close to the ground or water surface, and it has broad application prospects. To extend the cruise duration of WIG, a numerical investigation on flow control over a two-element airfoil under the ground effect was conducted using a dielectric barrier discharge (DBD) plasma actuator. The influence laws of ground effect on the control performance of plasma actuation were obtained, and the coupling mechanism between the ground effect and the plasma actuation was clarified. From the aerodynamic perspective, the lift enhancement effect of plasma actuation is closely related to the ground clearance of the airfoil. As the ground clearance increases, the lift augmentation effect undergoes a process of slow increase, rapid increase, and then stabilization. On the other hand, from the perspective of flow field, before actuation is applied, the ground effect suppresses the shedding and dissipation of the wake vortices of airfoil, resulting in prolonged vortex shedding trajectories, increased duration, and decreased shedding frequency. After actuation is applied, the plasma actuator interacts with the flow field via induced vortices, and achieves separation flow control by injecting momentum into the boundary layer, and transmitting disturbances. Overall, the ground effect weakens the control effect of plasma actuation. The control effect under near-ground effect conditions exhibits the characteristics of "slow response and large-scale structures", while that under out-of-ground effect conditions shows "fast response and small-scale structures".