The application of plasma discharge to hypersonic flow control methods has received a good deal of research attention in recent years. As a fundamental study for such methods, direct current plasma discharge in Mach-7 hypersonic flow over flat plate was investigated both with wind tunnel experiments and numerical analyses. Impulsive discharge in a boundary layer over flat plate caused a decrease in the wall pressure around electrodes. For the purpose of clarifying the principal cause of this phenomenon, a numerical analysis was conducted by solving the three-dimensional Navier-Stokes equations with impulsive energy addition to the flow. Numerical results revealed that the pressure oscillates in the vicinity of heated region, which suggests that the fluctuation of surface pressure observed in the experiment could be qualitatively explained as the unsteady response of the flow to the impulsive Joule heating by the discharge. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.