Abstract: Sound field distribution of broadband array is calculated using acoustics finite element method(FEM)plus boundary element method(BEM).FEM-BEM model is established for the plane nine elements array,numerical method of calculating mutual radiation impedance among the transducers is given,the varying laws of mutual radiation impedance influencing acoustics performance is analysed among the transducers,directivity and beam width is calculated at three resonance frequencies.A broadband dense plane nine elements array is developed applying triply resonant transducers, the input impedance and directivity is measured in anechoic water tank.The results show that it is reasonable to lay array according to the half wavelengh of the first resonace frequency of the element,the numerical solutions agree with the measurement results well,which indicates the FEM-BEM method is feasible to calculate sound field distribution and analyse mutual impedance.