Abstract: The article presents a spotlight SAR imaging algorithm for large scenes.Based on the classical chirp scaling algorithm,the algorithm divides the datum into several sub-apertures to image.Squinted equivalent range model is used.Range scaling is combined with range compression.Rational scaling factor is selected to remove the difference of sub-apertures.Phase compensatory factor is(amended) to make azimuth time outstanding.After azimuth compression,the sub-apertures are arrayed and synthesized to offer a full-aperture resolution image.Validity of the algorithm is testified by computer simulations.