This paper describes investigations focused on the shock wave modification induced by a plasma actuator flush mounted on a cylinder in rarefied flow regime. The experimental measurements were carried out in a supersonic low-density wind tunnel and the numerical investigation used a 2D fully compressible Navier Stokes simulation. Experimental observations showed the modification of the shock wave when the discharge was switched on. The numerical simulations show that this modification cannot be reproduced correctly by thermal effects. A theoretical approach was then proposed, in which the shock stand-off distance is written as a function of the ionization degree of the plasma. This approach was confirmed experimentally by measuring electronic properties of the plasma.