Abstract: In the era of absence of realistic downward-looking array synthetic aperture radar (SAR) system, the difficulties in data acquisition and further imaging algorithms research have been brought about. So the research of downward-looking array SAR three-dimensional (3D) simulation has great significance. In order to restore the aircraft's real flight path and to verify the topographical mapping ability of array SAR technology in high-rise buildings, the traditional simulation research based on the assumption of uniform linear motion is abandoned. And the non-ideal trajectory motion error model of MIMO(multiple input multiple output) downward-looking array SAR is analyzed and constructed with high-abrupt urban buildings. The 3D range-Doppler (RD) imaging algorithm of urban buildings MIMO downward-looking array SAR under non-ideal trajectory is proposed. Then the flight path and attitude modeling simulation technique of the aeronautical platform, and a fast and efficient echo simulation technique are used to carry out simulation experiments. The correctness and effectiveness of the imaging algorithm are verified by the imaging results.