Abstract: The outer cavity Janus-Helmholtz with sound insulating layer is presented for obtaining the capacity of high-power non-directional transmitting. The radiation efficiency and directivity in the 0 degree direction can be improved when the radiation mode is changed by laying sound insulation layer. The operating bandwidth can be expanded effectively by the dual mode coupling between the fluid cavity vibration and longitudinal vibration of Janus transducer. A prototype that operate band between 1.1 kHz and 3.5 kHz is designed by the finite element method. Test results show that the results are in good agreement with the design. Compared with the inner cavity, acoustic radiation ability of outer cavity Janus-Helmholtz underwater acoustic transducer in the 0 degree direction has been significantly improved.