The main aim of this paper is to elucidate the mechanism of massive separation control by using a dielectric barrier discharge plasma actuator (DBDPA). A technique of design exploration is applied to find good operating-parameter combinations for the DBDPA. We consider a NACA 0015 airfoil with 16° angle of attack and Reynolds number Re = 63000. The flow without the control is massively separated, however we can suppress the separation using the DBDPA with the relevant operating parameters. Using good parameter combinations obtained by design exploration technique, the nature of the flow around the airfoil with and without control is explored in detail.