Due to the existence of mutual radiation between array elements, the performance of dense array will change, such as resonance frequency drift, radiation power reduction, etc., which will adversely affect the overall performance of the array. In this paper, the characteristics of the mutual radiation impedance of eight-element planar array are analyzed, and the radiation power of the array is improved by changing the mutual radiation impedance. By introducing the interaction of the mutual radiation into the calculation of the directivity, the directivity calculation of the array is amended. Based on the above analysis, the finite element software is used to simulate the directivity of the array, and a prototype is made for test. The result shows that the lower the frequency and the smaller the space between the array elements, the stronger the mutual radiation between the elements, and the directivity of the array introduced into the amended mutual radiation is closer to real situation.