The problem which exists in most audio directional system is that the sound quality can not meet the application requirement. Piezoelectric transducers are often used in the system to generate audible sound with high directivity. The equivalent circuit model of the transducer is built and an efficient power amplifier is designed. Besides, the impedance matching network is also designed and optimized. The total harmonic distortion (THD) arose from the matching network has been analyzed from both the theory and practice. The effect of Q value of the matching network on THD has been determined. The proposed method can be used to reduce THD and improve the audio performance in the audio directional system.