Plasma flow control can significanrly improve the aerodynamic characteristics of aircraft and engine through nanosecond discharge plasma aerodynamic actuation.For the practical purposes,plasma flow control is assumed to be used mainly at altitudes of 10-20 km,at which the static pressure (40-185 Torr) is much lower than the atmospheric pressure.This paper reports an experimental study of surface nanosecond discharge plasma characteristics at different operating pressures ranging from 2 Torr to 760 Torr.As the pressure decreases,the N2(C3Πu) rotational temperature remains almost unchangect while its vibrational temperature decreases initially and then increases.In addition,the discharge mode changes from a filamentary type to a glow type at 50 Torr.In the filamentary mode,the electron temperature remains almost unchanged.In the glow mode,however,the electron temperature increases remarkably while the pressure decreases.