Abstract: A new and powerful method for detecting moving targets in a synthetic aperture radar（SAR） image is presented. Phase errors induced by many moving targets are largely quadratic, which provides a basis, by way of a change in the Doppler rate, for estimating the combined effects of azimuth constant velocity and radial acceleration. In this paper, the data in the SAR image is corrected by subtracting the quadratic phase error, and inverse changed by adding the same quadratic phase for comparing, both results are transformed to time domain, where the fixed background clutter have same image intensity. The absolute value of subtracting the two signal expected to have superior moving target detection performance. The experiment result prove this method is valid.