Abstract: The sound pressure levels in the cavity of the high pressure microphone calibrator affected by the variation of the front cavity volume of pressure microphone are calculated and measured. A method of calibration is described in this paper. The result shows that different front cavity volumes of microphones will result in different sound pressure levels in the cavity of high pressure coupler at the frequency range and the same insert voltages of the calibrator. Neglecting the correction as a result of the effect of the front cavity vlolume will cause an error of a couple of decibels. Volume of high pressure coupler has been measured using a standard condenser microphone with known front cavity volume and a laser-vibrometer. Calibrations of the high pressure microphone calibrators are performed by measuring the amplitudes of the piston of the calibrator using laser-vibrometer at the sound pressure levels of 124 to 164 dB re. 20 μPa with an accuracy of ± 0.27 dB.