Abstract: The array mode of linear distributed array and the change of azimuth pattern caused by it are briefly analyzed aiming at the imaging of linear-array synthetic aperture radar(SAR) system in near space. Based on the request of SAR imaging, the effect of imaging performance is analyzed by the sparse sub-array mode of distributed array, including the noise equivalent sigma zero and the azimuth-ambiguity-to-signal ratio. The simulation results prove that the array mode, sub-array azimuth aperture and sub-array spacing of the SAR system should be optimized according to the system performance index to meet the quality of linear-array SAR imaging system in near space.