A modified method is proposed for acoustic array directivity calculation. in this method, a series of solution for mutual radiation impedance between array elements has been obtained, the radiation sound field of the array is modified considering mutual radiation impedance, and a new formulation for array directivity calculation is derived from that modification. simulation examples show that there are notable differences between cases of considering and ignoring the mutual radiation impedance in array directivity calculation. the consideration of mutual impedance effects is necessary in acoustic array directivity calculation.