The present disclosure includes a method for optical measurements. The method includes providing a substrate with a structure for optical measurement on the substrate; and illuminating a light spot on the structure for optical measurement to obtain a measured light scattering spectrum. The method also includes performing a first matching process to obtain a plurality of matching standard optical scattering spectra and a plurality of first matching degrees, each standard optical scattering spectrum corresponding to one first matching degree; obtaining a plurality of combined optical scattering spectra based on the plurality of matching standard optical scattering spectra; and performing a second matching process to obtain a plurality second matching degree, each corresponding to one combined optical scattering spectrum.