Abstract: To reduce the length of outboard-driven class IV flextensional transducer and to improve the practicality, a solution of setting a U-shaped groove at the macro axis of the ellipse shell and appending the driven unit into the bottom of the groove is presented. How the size of the groove affects the transducer's resonant frequency and volume displacement is analyzed especially with the help of finite element software. Furthermore, according to the transmitting voltage response of the underwater model, an outboard-driven class IV flextensional transducer with a resonant frequency at 2.2 kHz and a bandwidth of 330 Hz is designed. Beside having the advantages of the existing outboard-driven class IV flextensional transducer, this new structured transducer can also remedy the weakness of the traditional one in size too large.