Disclosed are an auto exposure system and a method thereof. The auto exposure system may check whether an exposure target value is correct using brightness information of an input image. When the exposure target value is not proper, the auto exposure system may readjust the exposure target value through analyzing the brightness information of the input image. Also, the auto exposure system may correct exposure of the input image based on an exposure correction value according to the adjusted exposure target value, thereby adjusting the exposure of the input image to be proper. Also, exposure information of the input image may be easily obtained from a final exposure target value.