Stability constant logK, which tested three kinds of soil soluble humic acids reacted with copper ion to form the complexes,
appeared in the following tendency;darkcultivated loessal soil＞old manured loessal soil＞yellow loessal soil. logK value was related to pH,temperature and ionic strength. The thermodynamic function variations in complexation were :△rGm θ＜0,△rHm θ＜0, and △rSmθ＜0, showing that the complexation reaction was a spontaneous exothermic reaction and that negative value of △rSm＜0 was in the same sequence with logK, wich was considered as the entropy effect of humic acid molecular deformation and complex stability in process of humic acid reaction with copper ion. Freundlich equation, single surface hangmuir equation and double surface Langminrequation were used to describe copper ion adsorption isotherms of different soil insoluble hamic acids. Thermodynamic function variations in adsorption process were; △Gmθ＜0, △Hmθ＜0, and △Smθ＞0, suggesting that adsorption was a spontaneous, exothermic and increasingly confused process. △Smθ value could characterize the entropy state of copper ion at surface of humic acid. Structure of copper ion adsorption at humic acid surface was similar to the diffuse electric double layer structure.The differences of characteristics between adsorption and complexation were closely related to their different compound mechanisms.