Abstract: To the effect of mutual impedance on array's radiation power,the radiation impedance of an underwater transducer array is computed;the mutual radiation resistance characteristics of two elements array is analyzed,the effect of mutual radiation is quite strong and disciplinary when element's radius is less than λ/2 but very weak when element's radius is bigger than λ/2;the mutual radiation resistance characteristics of two elements array,uniform linear array and N×N plane array are analyzed,the optimal design for higher radiation power of an array in which the element's radius is less than λ/2 is done.The result shows that: when element's radius is less than 0.22λ,the compact arrangement is the optimal one;when the radius of elements is bigger than 0.22λ,the distance of neighboring array elements should be 5λ/4.