Abstract: The influence on low-frequency spaceborne synthetic aperture radar (SAR) azimuthal resolution is analyzed, which is caused by ionospheric scintillation effects, and space-variant scintillation phase errors are generated by 2-D phase screen method. For the conventional phase gradient autofocus (PGA) method couldnot correct the 2-D space-variant phase errors in SAR image, this paper proposes a method that divids the whole image into several sub-aperture images in range direction based on a certain rule. Using the conventional PGA to estimate the phase error of every sub-aperture image, these sub-aperture phase errors are interpolated to get the whole image's phase error. The simulation results show that compared to the conventional PGA method, the sub-aperture PGA method can effectively resolve the two-dimensional space-variant scintillation phase error influences on the image azimuthal resolution, and the image is recovered after correction and the azimuthal resolution is obviously improved.