The present disclosure provides an optical substrate and a display device. The optical substrate includes: a light guide plate which includes a light entering surface and a light extraction surface adjacent to the light entering surface, and is configured to enable light entering the light guide plate through the light entering surface to be totally reflected toward an opposite surface of the light guide plate opposite to the light entering surface; and a plurality of light extraction structures which is arranged on the light extraction surface of the light guide plate for extracting the totally-reflected light in the light guide plate, and has areas of orthogonal projections of the plurality of light extraction structures on the light extraction surface of the light guide plate gradually increasing along a direction from the light entering surface to the opposite surface.