Provided are a method and device for measuring a critical dimension of a nanostructure. The method includes acquiring a reference intensity distribution, in each of a number of spectral bands, of light scattered by at least one reference nanostructure, for each of a number at different positions of the at least one reference nano structure disposed along an optical axis; generating a library of reference intensity distribution arrays based on a number of the reference intensity distributions, determining an intensity distribution of light scattered by a nanostructure under investigation, for each of the number of spectral bands, at each of the number of different positions of the nanostructure under investigation disposed along the optical axis; generating an intensity distribution array by using the determined intensity distributions, and determining information about a critical dimension of the nanostructure under investigation by comparing the intensity distribution array with the library of reference intensity distribution arrays.