Abstract: The working bandwidth of four-sided type flextensional transducer is usually narrow, and for improving bandwidth capability, vibration and radiation characteristics of the four-sided flextensional transducer are discussed, and influence from shell structure parameters to transmitting voltage response is analyzed emphatically. According to the analysis results, a bandwidth realization method is proposed. Then simulation calculation is carried out with finite element software, and a prototype of four-sided type flextensional transducer is developed. The transmitting voltage response of the transducer gets to 140 dB with fluctuation less than 4 dB from 2.4 kHz to 5 kHz. The finite element simulation and experimental results are in good agreement. It is proved that the designed four-sided type flextensional transducer not only can work in low frequency, but also may transmit high power in small size. In addition, the four-sided type fiextensional transducer owns broadband transmission characteristic.