We developed a fundamental testbed and investigated the suitable transducer for the wireless power transmission (WPT). We also had 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 by its structure and the electric impedance of the transmitter and receiver by matching networks. In this paper, we investigate the transducer (DEV) for improving the transmission 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% compared to our previous report. In addition, we manufactured designed transducer, and confirmed the system's efficiency is about 50 % experimentally. This result also suggests that WPT by the acoustic wave be practicable.