Abstract: Abstract：Objectives Aiming at the problems of difficult balance between accuracy and efficiency, excessive grid density under high-frequency incidence, and large resource consumption in the calculation of RCS of large-scale array antennas, a subarray extrapolation method for large array antennas based on Gordon's integral method is proposed. According to the full-wave simulation results of small-scale subarrays, the RCS of large array antennas can be extrapolated efficiently and accurately. Methods Based on the differences in the positional attributes of array elements, the array is divided into different typical units, and the aperture field of the subarray unit is extracted in different regions. Gordon's integral method is introduced to transform the two-dimensional surface integral into the line integral along polygon boundaries, so as to accelerate the near-far field transformation, reduce the grid density, and improve the calculation efficiency of equivalent surface currents. The spatial extrapolation mapping of the scattering characteristics is realized by the phase correction factor, and finally the total scattering field of the target array is obtained. Results For Vivaldi array antennas and multi-layer stacked patch array antennas, the results of monostatic and bistatic RCS extrapolation are verified respectively. Compared with the full-wave simulation results, the calculation speed is increased by 3 times while the relative root mean square error is less than 5%. Conclusions The RCS extrapolation method proposed in this paper has both high calculation accuracy and good operation efficiency, which can provide an efficient and reliable calculation method for RCS calculation of large array antennas.