A method for measuring light intensity distribution includes the following steps that a carbon nano tube array arranged on one surface of a substrate is provided, placed in an inert environment or a vacuum environment and provided with a first surface far from the substrate; a light source to be measured is used for irradiating the first surface of the carbon nano tube array, so that the carbon nano tube array irradiates visible light; a reflecting mirror is provided, so that the visible light irradiated by the carbon nano tube array is reflected through the reflecting mirror; an imaging element is used for performing imaging on the visible light reflected by the reflecting mirror, and the intensity distribution of the light source to be measured is read.