To explore new methods of broadening the working bandwidth of tonpilz underwater transducer with double excitation, Equivalent circuit method and finite element method were used in analyzing transducer’s vibration modes. The effect of the mass with different materials and lengths between the two series of piezoelectric ceramics was studied. A new way of broadening working bandwidth which combines the longitudinal vibration at lower frequencies , longitudinal-radial-flexural vibration at higher frequencies was presented. After simulating and optimizing the structure of the transducer with finite element method, a sample with working band of 14 kHz to 47 kHz was made and tested. This method was demonstrated to be useful in broadening the working bandwidth of tonpilz transducer with double excitation.