In this paper, we present the interlaced fast Fourier transform (FFT) method to parallelize the adaptive integral method (AIM) algorithm for the radar cross-section (RCS) computation of large scattering objects in free space. It is noted that the function obtained after convolution is smoother as compared to the original functions. Utilizing this concept, it is possible to interlace the grid current and charge sources in AIM and compute the potentials on each set of interlaced grid independently using FFT. Since the potentials on each interlaced grid are smooth functions in space, we can then interpolate the potentials to every other nodes on the original grid. The final solution of the potentials on the original grid is obtained by summing the total contributions of all the computed and interpolated potentials from every individual interlaced grid. Since the potentials of each interlaced grid can be computed independently without much communication overheads between the processes, such an algorithm is suitable for parallelizing the AIM solver to run on distributed parallel computer clusters. It is shown that the overall computation complexity of the newly proposed interlaced FFT scheme is still of O(N log N).