Abstract: The first three resonant frequencies and vibration modes of a novel flextensional transducer are calculated by finite element method, and compared with measured values. The advantage for use as underwater source are discussed. In addition, tre characteristics of computer program are described. It is pointed that the relation vector of voltage-equivalent driving node force conforms with that of current-node velocity in the discrete equation of finite element method, then the more convenient equation is obtained. The unified processing method of axisymmetrical and plane problems and the method convenient for computer to calculate the antiresonant frequencies are explained.