Abstract: In this paper, the reason causing the phase error to be produced by Chirp Scaling Algrithm are analyzed, The consequences resulting in phase error of the effective radar range, coherent integral angle and the relative bandwidth of the signal and its influence on imaging quality are analysised, and only on the condition of the near radar range, small cohenrent integral angle and narrow relative bandwidth of the signal, the Chirp Scaling Algorithm can be used correctly for Synthetic Aperture Radar(SAR) imaging. Finally, the conclusions are tested by computer simulation.