In the process of heterogeneous photo-catalytic degradation, the reaction rate depends strongly on the property of organic binding on the surface. It is important to identify the adsorption of organic compounds on TiO_2 surface to understand the mechanism of degradation and proper kinetics expression. The infrared spectroscopy was used to analyze the methyl orange adsorption on TiO_2 surface in aqueous solutions in different pH ranges. The variation of the surface complexation of methyl orange formed on the TiO_2 surface in different acid and basic media was discussed. And the adsorption amounts were also qualitatively analyzed. Methyl orange has strong, weak and little adsorption on the TiO_2 surface in acid, basic and near neutral solution, respectively
