The spectral characteristics of radio frequency (RF) discharge plasma were studied at a static air pressure of 12 kPa (pressure corresponding to supersonic wind tunnel section). The effect of RF discharge plasma actuation on unsteadiness of shock wave/boundary layer interaction was studied in supersonic air flow with Ma of 2. The experimental results show that, the relative spectral intensity representing electron temperature rises with the increase of loading power at the same actuation frequency, while the relative spectral intensity representing vibration temperature and electron density hardly changes. When the loading power remains unchanged, as the actuation frequency increases, the relative spectral intensity representing electron temperature increases first and then decreases, however, the relative spectral intensity representing vibration temperature and electron density doesn’t change significantly. The dominant frequency of shock wave oscillation is low frequency without plasma actuation. After applying radio frequency discharge plasma actuation, the low-frequency oscillation of shock wave is weakened and the high-frequency oscillation is strengthened; the characteristic frequency of shock wave changes from low frequency to high frequency; high-energy vortex appears in the boundary layer.