Abstract: Based on hybrid method of finite-difference time-domain (FDTD) and time-domain physical optics (TDPO), this study applies sparse sampling to near- and far-field calculations to improve the efficiency of large aperture reflector antennas computation. In the conventional hybrid method, near-field of feed to far-field of reflector antenna transformation has largest calculation amount, and it will be reduced by sparse sampling optimization method. This method samples at intervals on time domain and space which is much faster. The example of large parabolic antenna whose aperture size is 100 wave length fed by horn is given. Comparing with the results of traditional method, the maximum relative error is only −36.03 dB, while the time is reduced to 2.51%. The computing results are in good agreement with those by CST software, the time is reduced by 93.18%, which demonstrates that the proposed method has small error and high computational efficiency.