A display panel and a manufacturing method thereof, and a display device. The display panel includes a light guide plate, an array substrate, a liquid crystal layer between the light guide plate and the array substrate, a plurality of light-extracting gratings located on one side of a light exit surface of the light guide plate, and a transparent protection layer between a film layer where the light-extracting gratings are located and the light guide plate. The light guide plate includes a plurality of light-extracting port areas, and transparent areas besides the light-extracting port areas; each light-extracting port area is provided with one light-extracting grating; the protection layer is at least provided on the transparent areas, and the protection layer is configured to prevent the light guide plate in the transparent areas from being excessively etched to form a plurality of depressions.