Abstract: The raw data of Synthetic Aperture Radar (SAR) is complex value, as well as the image data. Due to the random phase of each scattering cell, continuous scene has a wide signal band which makes single-aperture SAR difficult to realize down-sampling. In this paper, imaging model of cross-track sparse array SAR is analyzed. Signal reconstruction based imaging method under cross-track multi-aperture structure is investigated to eliminate random phases of scatters and reduce the signal bandwidth. Consequently, sparse array side-looking 3D imaging with larger interval space sampling is realized. The results on InSAR 2D real data verify that the bandwidth can be reduced after signal reconstruction. Besides, the simulation experiments on 3D imaging validate the effectiveness of the proposed method.