A new technique is proposed for analysis of the composition of incident ion beam accelerated by Van de Graaff electrostatic accelerator for a purpose to analyse of effects of ion beam composition on a forming energy backscattering spectrum. The procedure is based on the energy distribution of neutral fraction of the hydrogen ion beam by silicon surface detector and susecquent recovering of the primary spectrum for H+ fraction. Recovering ion beam energy spectra are used for numeric simulating (using models of the one-fold and two-fold scattering) of process of elastic backscattering from thin gold film.