Abstract: In consideration of the mutual coupling, the active element pattern (AEP) theory is adopted to calculate the time-domain radiation field of large pulsed antenna arrays. The AEPs of a large array can be transformed into those of a small array under similar mutual coupling condition, and the radiation field of the large array is obtained by superposing AEPs of all the elements. On this basis, an improved method is proposed combined with time-domain radiation theory. By formula deriving, the analysis of a large linear array or a large planar array can be respectively converted into that of two small linear arrays or four small planar arrays. In comparison with the original method, calculating all AEPs of subarray is avoided. A 13 linear array and an 1113 planar array are calculated for verification, the results agree well with software simulation results. Compared with the original method, the calculation is reduced by 56.8% for the linear array and 81.17% for the planar array.