In a method for testing an aperture of the image capturing device, a brightness value range of images is divided into a plurality of range intervals, and one of the range intervals is determined for testing the aperture. A brightness value of a current image captured by the image capturing device is calculated. A diameter of the aperture is controlled to increase or decrease to change the brightness value of the current image to be within the determined range interval, if the brightness value is not within the determined range interval. After the brightness of the current is changed to be within the determined range interval, if the brightness value of the current image has been changed during a predetermined time period, it is determined that the aperture does not work normally.