Mn-based　catalysts　extremely　restricted　with　the　deactivation　by　SO2.　In　this　paper,　catalysts　of　Mn/TiO2　prepared　by　co-precipitation　method　for　low　temperature　selective　catalytic　reduction　(SCR)　of　NO　with　NH3　under　the　influence　of　SO2.　For　Mn/TiO2,　NO　conversion　decreased　rapidly　from　90%　to　about　55%　at　200　degrees　C　in　the　presence　of　SO2.　We　reveal　the　mechanism　of　SO2　effect　on　the　adsorption　of　NH3　and　NO　based　on　DRIFT　and　TPD.　The　result　show　that　SO2　can　reduce　the　adsorption　amount　of　NH3　on　the　Lewis　acid　sites　and　react　with　NH4+　to　form　NH4HSO3　on　the　Bronsted　acid　sites.　In　the　meantime,　SO2　can　inhibit　the　adsorption　of　NO　took　part　in　the　SCR　reaction　on　the　surface　of　catalyst　due　to　the　mechanical　of　competitive　adsorption.　These　poisoning　phenomenon　of　SO2　hinder　the　proceeding　of　SCR　reaction.