The experiment studied: The saturated adsorption and desorption of the 3 types (A, B, C ) of agricultural humic acids for K+, and the effects of pH on the adsorption and desorption. Results showed that: Compared with A and B, potassium-saturated humic acid C exhibited stronger adsorption and desorption activities of its cation exchange capacity (CEC) 375.74 cmol/kg, the maximum desorption 71.00 mg/g. Besides, in the first 60 min of desorption reaction the capacity of desorption was very close to the maximum; the properties of humic acid A, B were similar in their K+ adsorption capacity. The adsorption saturation was reached in the first 60 min for humic acid A, and the adsorption quantity per unit was 10.2 mg/g. The adsorption saturation was reached in the first 20 min for humic acid B, and the adsorption quantity per unit was 7.72 mg/g. However, the adsorptive rate of K+ for humic acid B was faster than A, and B could reach saturated adsorption in a shorter period of time. All of the 3 types of humic acid had a strong buffering capacity to adapt to the changes in the medium pH. With the rise of pH value, the adsorptive quantity for K+ of humic acid A and B decreased within the effective buffering range, but the desorption of K+ for humic acid C appeared to reach a plateau after an ascent in pH range of 35.