Abstract: A method for automatically focusing a projector includes a projection lens, a driver device and an image capturing device. The method sets an interval step according to a focusing range of the projection lens, reads a predefined picture from a storage system of the projector, and controls the projection lens to project the picture to a projection area. The method controls the image capturing device to capture an image of the picture from the projection area when the projection lens moves at every interval step, and analyzes a contrast of each of the images to determine an optimal image from the images. The method determines a current focus of the projection lens having the optimal image as an optimal focus of the projection lens, and drives the driver device to control the projection lens to move at the optimal focus.