[Objective] Hofmeister effects can be seen everywhere, and usually manifested as difference in behavior of covalent ions in solution. Hofmeister effects exist universally in physical, chemical and biological processes, playing an important role in interface interaction. Also, Hofmeister effects are of great scientific significance to ion exchange/adsorption process. The purpose of this paper is to compare Hofmeister effects on the adsorption processes of three kinds of alkali metal cations (Na⁺, K⁺, Cs⁺) on saturated surface of Cu²⁺montmorillonite and to analyze sources of the Hofmeister effects.[Method] An ion adsorption kinetics experiment was carried out using the constant current method to compare the three alkali metal cations (Na⁺, K⁺, Cs⁺) in adsorption on Cu²⁺-montmorillonite surface. The experiment was designed to have the temperature fixed at 298 K, and the binary mixed electrolyte solution composed of XNO₃ + LiNO₃, where X stands for Cs, Na or K. The two electrolytes in the mixed solution was equal in concentration, 0.0001, 0.001 or 0.01 mol·L^-1. In the end, ion-surface Hofmeister energies and apparent charge coefficients were worked out in line with the Gouy-Chapman theory.[Result] (1) The adsorption of Na⁺, K⁺ and Cs⁺ on the surface of Cu²⁺-montmontmoillonite showed a first-order kinetic process under a weak electrostatic force, with average adsorption rate and equilibrium adsorption demonstrating obvious Hofmeister effects in an order of Na⁺ < K⁺ < Cs⁺. For example, when the electrolyte was 0.01 mol·L^-1 in concentration, the average adsorption rate of Na⁺, K⁺ and Cs⁺ on the surface of Cu²⁺-montmorillonite reached 4.48, 8.68 and 11.74 mmol·kg^-1·min^-1 respectively, and the equilibrium adsorption did 129.17, 341.11 and 911.47 mmol·kg^-1respectively in amount within 27 minutes. (2) Hofmeister energy increased with decreasing electrolyte concentration. On the surface of Cs⁺-clay mineral, Hofmeister energy was the main contributor of the interaction, while on the surface of K⁺/Na⁺-clay mineral, classical Coulomb energy was. When the electrolyte concentration was 0.0001, 0.001 and 0.01 mol·L^-1, the ratio of w_Hi (0)/w_Ti (0) of Cs⁺ was 67.00, 65.71 and 58.00%; that of K⁺ 44.24, 43.36 and 42.19%; and that of Na⁺17.88, 9.29 and 8.82%, respectively. (3) Effective charge coefficient decreased with increasing electrolyte concentration. This is because increased electrolyte concentration compresses the electric double layer, thus enhancing its capability of shielding the electric field, and leading to decrease of the electric field in the diffusion layer in intensity, which eventually weakens polarization of the adsorbed ions and reduces effective charge coefficients. The non-classical polarization significantly amplified apparent charge coefficient of the ions. The apparent charge coefficients of Cs⁺, K⁺, Na⁺ worked out in this experiment under the condition of the electrolyte concentration being 0.0001, 0.001, 0.01 mol·L^-1 followed the sequence of Cs⁺ > K⁺ > Na⁺ in Hofmeister effect. Apparent charge coefficient of Na⁺, K⁺ and Cs⁺ increased from the standard +1 value to +1.14, +1.76 and +2.78, respectively.[Conclusion] This study clearly demonstrates that the Hofmeister effects originate mainly from the difference in ion-surface interaction energy between the ions caused by their non-classical polarization. And all the findings in this study provides a new idea for elucidating the mechanisms of interface reactions in such a unique system as soil.