The structure of n-hexadecyl o-xylene sulfonate sodium was optimized by GAMESS(US). The aggregation behavior was simulated at the oil/water interface by molecular dynamics simulation, strong hydrogen bonds exits between the oxygen of the sulfonate and the hydrogen of the water, therefore the first water layer and second water layer are being formed, the counter-ion sodium are distributed between the first water layer and second water layer. The increase of the surfactant have not effects on the hydrogen bond distribution which is formed from the water and the surfactants. n-Hexadecyl o-xylene sulfonate sodium have strong affinities with the decane at the oil/water interface, which indicates that it can reduce the interfacial tension between the water and the crude oil.