Abstract: The sensitivity of transducer should be an important characteristic in the field of NDT. But so far, no method for this measurement is available. In this paper the transducer is regarded as a plane source and the reciprocity parameter is derived under the far-field. The method for the calibration of ultrasonic transducer is presented with the reciprocity technique and the measurements are carried out in a solid sample. Experiments show and confirm that the transmitting and receiving sensitivities of the transducer applied to NDT can be exactly measured. The precision of the measurement is within 1 dB under certain coupling condition.