Monte Carlo simulations were employed to study the argon adsorption on kaolinite surface with an experimental comparison. By (001) surface simulation, the low energy peak of isotherm derivative was clearly assigned to the hydroxyl surface, and the high energy peak to the basal oxygen surface. The monolayer adsorption mechanism and the adsorption sites were made according to the distribution and potential of argon on both (001) surface. By simulations of (100) and (010) lateral surfaces, and complete outer surface, the difference between (001) surface simulation and experimental results was clarified and a new destination for derivative peaks was proposed.