The present invention provides a method for automatically focusing applied to a camera module. The method comprises the following steps: (a). determining a value of a modulation transfer function of an image at a center area and four corner areas of a lens by a processing unit; (b). determining whether the number of times of decreased or unchanged of the value of the modulation transfer function at the center area is over a predetermined value; and (c). if over the predetermined vale, then determining the average of the value of the modulation transfer function at the four corner areas by the processing unit, to determine the maximum of the value of the modulation transfer function at the center area.