Abstract: Aiming at the problem of the large number of array elements and low utilization rate of the three-dimensional synthetic aperture radar (3D -FDA-SAR) imaging method of frequency diversity arrays, a 3D -FDA-SAR imaging method based on multiple input and multiple output arrays is proposed. The frequency diversity array of 3D -FDA-SAR tangent track direction is changed to multiple -input multiple -output frequency diversity array. The multiple input multiple output frequency diversity array moves with the moving platform to form a synthetic aperture along the track direction, combined with the tangent track direction The real array is combined with a virtual two-dimensional frequency diversity array plane to obtain the downward-looking three -dimensional imaging capability of the target. Firstly, a multi-input multi-output 3D -FDA-SAR imaging model and signal model are established, using multi-input multi-output technology, the waveform quadrature signal single-frequency narrowband signal is sent at the transmitting end, and all the transmitting arrays are received through the full-frequency receiving mode at the receiving end. The echo signal reflected by the target is separated by a quadrature matched filter to obtain the echo data of different receiving and sending channels, and then the echo data is imaged by the backward projection algorithm, and finally the three -dimensional imaging result of the target is obtained. Experimental simulation results show that the 3D -FDA-SAR imaging method based on multiple -input multiple -output arrays uses a small number of array elements, improves the utilization of the array elements, and obtains the three -dimensional imaging capability of downward-looking targets.