Using Octadecyltrimethylammonium (OTA) cations with long carbon chain to intercalate into Na-montmorillonite samples, the change of adsorption amount and adsorption state of OTA with the retention time was investigated. The sdudy on the reaction kinetics for the alkylammonium adsorption in the montmorillonite interlayers showed that the isothermal adsorption behavior fit in with a second order reaction kinetics equation. Reaction rate constants had great differences with application force of adsorption process. OTA in the montmorillonite interlayers through re-arrangement constantly at different time, adsorption state of OTA are analysised by XRD and FTIR. The interlayer spacing and diffraction peak relative intensity of montmorillonite/OTMA complexes shows a dynamic change, the alkyl chain conformations can change from “liquid-like” to “solid-like” with the reaction time. The arrangement of alkylammonium cations are more orderly.