The invention discloses an automatic focusing method for a projector, and the method comprises the steps: dividing a focusing image obtained at a plurality of focal length positions into a plurality of image regions, and dividing each image region into a plurality of sub-regions; calculating to obtain a sub-region definition of each sub-region in each focusing image; normalizing a subarea definition of the subarea corresponding to the same position in each focusing image; and selecting a position corresponding to the focusing image with the maximum definition as a focusing position according to the sub-region definition after normalization processing, and focusing the projector. According to the invention, normalization processing is carried out on the sharpness of the subareas at the sameposition of each focusing image, the reliability of the sharpness of the whole focusing image for determining the focusing position is ensured, and the focusing accuracy of the projection image of the projector is further ensured. An automatic focusing method, device and apparatus for the projector and a readable storage medium have the above beneficial effects.