Abstract: The mechanism of SAR received data and the method of data processing are studied in this paper, to explore the causes of the phenomenon of SAR image edges aliasing. Analysis shows that the aliasing phenomenon is related to the signal characteristics of SAR received data and the matching compressing characteristics of linear FM signal. Similar to the matching compressing result of shorted linear FM signal, SAR image edges aliasing always arises in the result of SAR imaging for every SAR system which uses linear FM signal as its transmitting signal, and the aliasing region size of SAR image is just equal to the sampling numbers of half pulse duration both in azimuth direction and range direction, because echo samplings of SAR real data are truncated which nearby beginning and ending both of azimuth direction and range direction. The reliability of above conclusion was tested by processing result of RADARSAT-1 data and linear FM signal. Two methods are proposed to choose non-aliasing SAR image last in the paper.