A method for measuring intensity distribution of light includes a step of providing a carbon nanotube array located on a surface of a substrate. The carbon nanotube array has a top surface away from the substrate. The carbon nanotube array with the substrate is located in an inertia environment or a vacuum environment. A light source irradiates the top surface of the carbon nanotube array, to make the carbon nanotube array radiate a visible light. A reflector is provided, and the visible light is reflected by the reflector. An imaging element images the visible light reflected by the reflector, to obtain an intensity distribution of the light source.