An curve-fitting method for accurate determination of optical constants and thickness is presented for chalcogenide glasses thin films. Optical constants and thickness of nanomultilayer chalcogenide structure As2S3:Mn-Se were obtained by Swanepoel method from transmission spectrum using PARAV software. Proposed curve-fitting method is based on numerical simulation of transmission spectrum based on film parameters obtained by Swanepoel method and comparison one with experimental transmission spectrum. It is shown that modeled spectrum is not fully corresponding to the original measured spectrum due to inaccurate absorption coefficient determination in the region of Urbach absorption. Adjusting of absorption spectrum with further numerical simulation of spectrum allows achieving the best correspondence to original transmission spectrum. It solves the problem of the accurate absorption coefficient calculation in the different absorption regions. Finally, dependencies of the absorption coefficient on wavelength of the nanomultilayer chalcogenide films structures were obtained from transmission spectra using the proposed method.