Abstract: An in-situ calibration method was developed in this paper.The acoustic pressure data from two calibrated microphones were utilized to calculate the sound field in ducts.Then the sensitivity of every microphone was obtained by comparison of the signal measured by every microphone with the sound field calculated above.The advantage of the current method is that all microphones can be calibrated simultaneously and the phase sensitivities of these microphones are also obtained.A calibration experiment has been conducted on flow impedance test rig(FITR),and the calibration results were compared with those calculated by the mode-matching method,showing a good agreement.Additionally,as every microphone's complex sensitivity can be obtained respectively at different frequencies,low-precision microphones can have better precision by being calibrated using high precision microphones.By using these calibrated microphones,the cost of experiment can be reduced obviously.