A viewing angle widening film, a manufacturing method thereof, and a display device are provided. A first film layer of the viewing angle widening film includes protrusions spaced apart from each other and extended along a first direction. The protrusions include a first protrusion and a second protrusion arranged on a side of the first protrusion away from a flat layer, a surface of the second protrusion on a side away from the flat layer is an arc surface, and a diffusion effect of the second protrusion is weaker than that of the first protrusion.