Abstract: Focused the issues on Moving Target Detection (MTD) in spotlight mode Synthetic Aperture Radar (SAR),the echo is divided into groups that are continuous and partly overlapping in time domain. Every group of data can be regarded as coming from a sub-aperture of time domain. The images of same ground scene are then generated in multiple sub-apertures. By Subtracting two consecutive sub-aperture SAR images, the stationary clutter or targets that appear in a sub-aperture SAR image can be suppressed or substantially eliminated, but moving target image is left. Superposing the result of subtracting every two consecutive sub-aperture SAR images, the tract of this moving target is obtained. Furthermore, its moving parameters can be estimated. This paper proved this method in theory and the simulation result testifies its validity.