The invention discloses a method and device for determining a position error of a synthetic aperture radar (SAR) carrier aircraft. The method includes the steps that at least two ground target points are selected according to radar return data; the range migration (RCM) track of each ground target point is detected; the position error of the SAR carrier aircraft is obtained through calculation according to each detected RCM track. The position error of the SAR carrier aircraft can be determined without the additional installation of a guided system, so that cost is saved.