We developed a fundamental testbed and investigated the suitable transducer for the wireless power transmission (WPT). We also reported experimental results of the transmission efficiency in water by using the commercial transducer (COM) which only designed to match to the acoustic impedance of water and the electric impedance of the transmitter and receiver. In this paper, we investigate the transducer for improving the efficiency based on the Mason's equivalent circuit. For deciding a structure and materials of the transducer, we used ANSYS well-known as the multi-physics simulator. In this result, it is confirmed that the transmission efficiency is drastically improved from less than 1% to 60%. In addition, we made designed transducer, and confirmed the systems' efficiency is about 50 %. This result suggests that the WPT by acoustic wave is practicable. © 2011 IEEE.