Samples of montmorillonite and clay fractions (＜2 μm) of black soil, yellow-brown soil, red soil, and latosol were used in the test to determine mean free binding energies (ΔG_bi) between monovalent cations Na⁺, and K⁺ and various clay particles with the ion activity method and the suspension Wien effect method. Results show that the values ofΔG_bi determined of Na⁺ to black soil, yellow-brown soil and montmorillonite with the two different methods were quite similar, and the relative errors ofΔG_bi determined with the ion activity method in relation to those determined with the Wien effect method varied in the range from 24% to 10%; the values ofΔG_bi determined of K⁺ to black soil, and yellow-brown soil with the two different methods were almost the same, with relative errors lingering below 2%. But the relative errors ofΔG_bi determination of red soil were about 11.5%. The results also indicated that the sodium glass electrode is applicable to this experiment only when the difference in pH between the standard solution and the suspension to be tested is less than 0.5; and the liquid-membrane potassium electrode can be used to determine K⁺ activity in the soil suspensions in this experiment, but can not in the suspensions of montmorillonite. However, it is still impossible to directly apply the Wien effect method to determination of binding energy of monovalent cations to the variable-charge soils, positive in charge, such as latosol.