Abstract: To address the issue of rotor airfoil aerodynamic performance degradation due to dynamic stall, we conduct experimental investigations utilizing pulsating pressure sensors and asymmetric configuration actuators with dielectric barrier discharge. The focus is to investigate the unsteady plasma flow control on the rotor airfoil dynamic stall. Particularly, we aim to explore the underlying mechanism of unsteady plasma control and its sensitivity to actuation parameters. The experiments have confirmed the promising control capabilities of unsteady plasma actuation. The results indicate that the unsteady flow control can effectively mitigate the sudden drop of airfoil lift, with a 20% duty cycle being sufficient to achieve significant control effects. A comprehensive parametric study on the dimensionless actuation frequency F⁺ demonstrates that the optimal performance of the unsteady control occurs at F⁺ = 1～2. This optimal condition yields a remarkable 16% reduction in the lift hysteresis loop area and a 6% increase in the average lift coefficient. Furthermore, by comparing the airfoil aerodynamic forces and pressure contours under steady and unsteady control modes, the control mechanism of the rotor airfoil dynamic stall based on the plasma actuation is analyzed. Notably, the plasma actuation primarily acts on the dynamic stall vortex shedding, while unsteady actuation significantly weakens the adverse effects of dynamic stall vortex shedding on the airfoil aerodynamic forces. Additionally, the unsteady actuation generates more vortices, thereby enhancing the recovery of the leading-edge reverse pressure gradient and the flow reattachment.