The K⁺ adsorption kinetics of Fluvo-aquic soil and Cinnamon soil under different K⁺ concentration were studied. The results showed: (1) adsorption rate decreased with the increase in adsorption, and the relationship between them could be described with significant linear regressive equations, indicating the adsorption were fit for the first order equations; (2) the apparent adsorption rate constant k_a and the product of k_a multiplied by the apparent equilibrium adsorption q_∞ were significantly Sinearly correlated to K⁺ concentration C: (3) the relationship between q_∞ and C conformed to Langmuir and Freundlich isothermal adsorption equations. Based on those results the K⁺ adsorption kinetics was deduced, leading to four kinetics parameters n、k₁、k₂、q_max independent of C. With n、k₁、k₂、q_max the apparent parameters and free energy change △G of adsorption could be worked out, and under certain conditions n、k₁、k₂、q_max could also be used to judge isothermal adsorption and reckon its parameters.