The basic task of mathematical processing of reflectance spectra is the calculation of the dielectric function of the substance, which describe response of a crystal to an external electromagnetic field. The most modern and perspective way of the solution of this task is the dispersion analysis [Lorentz model (LM)]. However LM requires large volume of computing works at phonons optimum parameters selection. The rapid computer facilities development promotes overcoming of this difficulty. However without application of effective methods of optimization practically it is impossible to execute DA for composite reflectance spectra. The efficiency GA strongly depends on such details, as a solutions coding method, genetic operations embodying, selection mechanisms, other algorithm parameters adjustment, success criterion. In this paper we offer modification GA for the solution of the reflectance spectra processing problem and results of the obtained algorithm work.