This paper proposes a new type high frequency broadband piezoelectric composite transducer and two methods which are composite materials and multimode coupling vibration have been used to expand the transducer bandwidth.The finite element modeling has been carried out with ANSYS software.The change rules that the resonant frequency and bandwidth change with the thickness,the height and the average radius of the piezoelectric ceramic ring have been obtained. Then we confirm the optimal design scheme of the piezoelectric sensitive element according to the simulation results. Two single composite piezoelectric ceramic rings were made according to the optimal processing parameters and finally we have fabricated a piezoelectric composite transducer by stacking the two different thickness piezoelectric ceramic rings.Through the test result, we found that the new type piezoelectric composite transducer have formed the dualmode coupled vibration and the bandwidth of the transducer can reach to 320~410 kHz with the -3 dB fluctuation of transmitting voltage response,its maximal transmitting sound level can reach to 147.8 dB. It proves that the bandwidth of the high frequency transducer can be greatly expanded by using composite materials and multimode coupled vibration.