The algorithm based on spectrum shift estimation is a processing method with brief flowchart and less processing time for improving range resolution in distributed small satellite synthetic aperture radar(DSS-SAR).But its performance is decreased by spectrum overlap and estimation error of spectrum shift.The influence of these two factors on the algorithm is analyzed in this paper.The mathematic expressions of the combination image

including the effect of the two kinds of errors

are deduced respectively

and the image quality worsening caused by the errors is discussed.The expressions and the discussion show that spectrum overlap decreases the peak side lobe ratio and the integral side lobe ratio of point targets

and the error of spectrum shift attenuates main lobe and increases the side lobe of point targets in the combination image.The point target simulation is employed to validate the analysis.Some suggestions are presented to improve the implementation of the algorithm based on spectrum shift

and a new concept of processing depth is proposed to enhance the practicality of the algorithm.