An image brightness correction method is described. First, a pre-flash is fired and a pre-flash image is shot. After a main flash duration is estimated according to the pre-flash image and an automatic exposure time of a camera device, a main flash is fired and a raw image is shot. Then, a brightness gain of the raw image is compensated according to a preset gain threshold, and a digital brightness gain of the image is adjusted to enable the image shot each time to achieve the same brightness gain.