Abstract: In order to improve the aerodynamic performance of high-altitude long endurance unmanned aerial vehicles (UAV) at low Reynolds numbers, experimental studies on flow control over a GAW-1 airfoil using a symmetrical dielectric barrier discharge (DBD) plasma actuator driven by a sinusoidal high-voltage power supply are carried out in a 0.5 m × 0.6 m low-speed wind tunnel with the help of force and pressure measurements. The formation mechanism of abnormal changes in drag is discussed and the controlling mechanism of flow control using the symmetrical DBD plasma actuator is explored. The chord length of the airfoil is 160 mm, and the Reynolds numbers based on the chord length are 8.3 × 10⁴ and 15.6 × 10⁴. The results indicated that the nonlinear variation of lift and the anomalous changes in drag that first increase and then decrease during low angles of attack at Reynolds number of 8.3 × 10⁴ are observed without plasma actuation. It is believed that the flow which maintains a pure laminar separation pattern over a large range of angles of attack, as well as a rapid transition from the pure laminar separation pattern to the trailing edge attachment pattern is the mechanisms for the nonlinear lift and the anomalous changes in drag. On the other hand, no evident changes in lift and drag at Reynolds number of 15.6 × 10⁴. In addition, the laminar separation shear layer becomes unstable under the influence of plasma actuation, and the flow status is changed from the completely laminar separation to a trailing edge attachment at lower angles of attack, leading to improve the lift and drag characteristics of the airfoil during lower angles of attack at low Reynolds numbers. Thus, the lift to drag ratio is increased by 87.9%. The present studies lay a technical foundation for improving the aerodynamic performance of high-altitude long endurance UAV.