As a new method for radar target feature extraction and recognition, microDoppler effect can express more kinematic information of moving targets. However, microDoppler will result in defocusing and other disadvantageous effect on SAR imagery, which can’t be overcome by conventional methods. Through the research of the vibration and rotation of SAR target echo model, SAR micromotion unified target distance equation and SAR echo are summarized in this paper, and azimuth will present Sinusoidal Frequency Modulation (SFM) characteristics of periodic signal. At last, simulation results on point targets validate the proposed approach.