The phase composition and local atomic and electronic structure of tin oxide layers have been studied by applying synchrotron X-ray absorption near edge structure spectroscopy. The inear combination analysis of the achieved results have been performed using ab initio calculated reference data for main tin-oxygen crystalline compounds. Our results suggest that proposed modelling approach successfully allows the reliable interpretation for Sn M4,5 X-ray absorption near edge spectra and appropriate atomic structure reconstruction and phase transformation dynamics in thermally oxidized tin oxide layers produced my magnetron sputtering.