Abstract: Side-looking three-Dimensional (3D) imaging of three-aperture sparse array Synthetic Aperture Radar (SAR) based on Compressed Sensing (CS) is investigated in this paper. Using the sparse array structure in cross- track direction formed by three aperture antennas, the elevation resolution can be obtained and 3D imaging is achieved. However, the conventional Fourier transform based 3D imaging approach has a low resolution in elevation direction and brings the image quality problem because of the low number of acquisitions and irregular space sampling. CS theory is introduced to improve the resolution in the elevation direction. Experiment results on simulation and real data validate the effectiveness of the proposed method compared with the conventional imaging technique.