Abstract: During the process of oil displacement, cationic surfactant can not only be used to lower the oil-water interfacial tension, but can be used to change the wettability of rock surface. In order to deeply understand the mechanism of action between cationic surfactant and sandstone surface, the ultraviolet spectrophotometry is applied to measure the adsorption capacity of cationic surfactant on the sandstone surface of different wettability, as well as the adsorption enthalpy is calculated according to related mathematical formula. The measurement indicates that the adsorption of cationic surfactant on sandstone surface accords with the Langmuir adsorption law. The saturated adsorption capacity of cationic surfactant on different sandstone surface varies a lot: the saturated adsorption capacity on oil sand surface reaches the highest, that on the oil wetted surface is moderate, and that on the water wetted surface is the lowest. The adsorption enthalpy is consistent with the adsorption capacity: the adsorption enthalpy on oil sand surface is the most, that on the oil wetted surface is moderate, and that on the water wetted surface is the lowest. This shows the action between cationic surfactant and oil sand surface is the strongest, which is favorable for changing the surface properties of reservoir rock and improving oil displacement efficiency.