A display panel and manufacturing method thereof and a display device are provided. The display panel includes: a base substrate, a light-emitting layer located on the base substrate, and a beam diffusion layer located on the side of a light-emergent surface of the light-emitting layer. The light-emitting layer includes a plurality of pixel units arranged in an array; and the beam diffusion layer includes a beam diffusion element corresponding to at least one of the pixel units, which is used to expand a light-emergent beam of the corresponding pixel unit. The beam diffusion element may expand the light-emergent beam of the corresponding pixel unit, which increases the area of the light-emergent surface of the pixel unit. Thus, the number of pixel units provided in a large-sized display panel may be reduced, the power consumption thereof may be decreased, and the occurrence of burn-in inside the display panel may be avoided.