Abstract:  Ultra wideband high resolution SAR imaging requires more accumulation of azimuth angle. In the wide beam case, there is a great difference between the lateral airborne platform disturbance error relative to the different azimuth beam target, and the motion error of airborne platform usually exist azimuth-variant. The azimuth variant error of motion compensation is difficult to be eliminated in SAR imaging, and this error Seriously affected the imaging quality. In order to solved this problem, this paper proposed a new method which would be accurately compensate this error. This method made use of echo azimuth corresponding relation between the spectrum and beam angle. By using the combination of DFT transform and motion error compensation this method can accurately remove phase error of different azimuth of target during azimuth spectrum forming. Experimental results demonstrated that this algorithm can effectively compensate azimuth variant error during the instance of high motion errors. The results show that the method can realize accurate imaging UWB SAR.