In this paper, a new wavefront curvature compensation method based on digital spotlighting preprocessing is proposed. First, digital spotlighting preprocessing, filtering and downsampling in 2 dimensional space domain, is performed on echo data. This generates multiple full resolution phase histories of smaller image patches, each corresponding to a narrow beam phase history data where the wavefront curvature effect can be ignored. Due to the inherent non planar motion compensation capability, PFA is used to produce focused fine resolution image for each small patch. Finally, all focused image patches are seamed together to get a full image. Simulation experiments show that the new algorithm has improved focused scene size when applying to phase history generated by non ideal radar flight path.