The invention relates to an automatic backlight adjusting device of a camera and a method thereof. The method comprises the following steps: the camera for shooting a moving image scans the pixels of a shot image by virtue of imaging elements such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) and the like, and then detects dark pixels with a low luminance level and bright pixels with a high luminance level; if the number of the dark pixels exceeds the preset stated number, a Delta luminance value is calculated by the luminance value of all the pixels minus the luminance value of the bright pixels; the Delta luminance value is taken as a standard to automatically execute backlight compensation movement; and if the number of the dark pixels does not exceed the preset stated number, the luminance value of all the pixels is taken as a standard to automatically execute backlight compensation movement so as to automatically distinguish backlight compensation movement executed under the condition of a large number of the dark pixels and backlight compensation movement executed under the condition of a small number of the dark pixels, and further execute backlight compensation movement which is more applicable to a shooting status.