Abstract: The Ma=1.98 experiment under asymmetric incoming flow was conducted to analyze the response of the wall pressure in an isolator when the shock train is subjected to a periodic motion at a low frequency.It was found that the isolator effectively isolates the periodic back pressures from the inlet.Wall pressure fluctuations are due to the propagation of wave fronts of the second acoustic mode.But they are subjected to an oscillating shock train in the most part of the shock oscillation region.Attenuation of wall pressure fluctuations in the shock oscillation region accords with the exponential law on the lower wall,and changes by wave shape and frequency of back pressure.It does not moronically decrease but fluctuate on the upper wall.