Behaviors of Cu²⁺ in adsorption-desorption in three variable charge soils and two constant charge soils as affected by its concentration were studied. It was found that the curves of pH and Cu²⁺ adsorption rate always intersected in the section of low pH, and the curves tendedd to lean towards the right when Cu²⁺ rose in concentration, and confirmed that in variable charge soils, adsorbed copper ions could be desorbed with deionized water and desorption peaks observed. The study on change in pH of the adsorption system as affected by desorption revealed that when the system adsorbing Cu²⁺ was lower than 5.0 in pH, its pH would rise after desorption of the ions, but when the system was higher than 5.0 in pH, ts pH would decline, which suggest that pH5.0 is probably another turning point where the mechanism of the soil adsorbing Cu²⁺ changes. Existence of weak adsorption state in specific adsorption and causes of its formation were also discussed.