This study mainly focused on the adsorption properties and adsorption mechanism of 2,4-D on two different humic acids. After the extraction of humic acid from the two different types of soil, the black soil and chestnut soil, adsorption experiments were carried out using the batch equilibrium techniques. Then FTIR and ESR spectral analysis methods were employed to explain the functional mechanism between 2,4-D and humic acid. The results showed the relationship between the amount of 2,4-D sorbed by the two humic acids and the reaction time, with the adsorption process for both acids being very fast at the beginning, then becoming slower and finally reaching equilibrium. The adsorption capacity of 2,4-D on black soil humic acid and chestnut soil humic acid were 0.39 and 0.42 mg·kg-1 respectively. More carboxylic acid structure made the initial adsorption rate of 2,4-D on black soil humic acid much faster than on chestnut soil humic acid. Adsorption isotherm of 2,4-D on the two humic acids was both in accordance with the linear model and the Freundlich model. The interactions between humic acid and 2,4-D are mostly weak forces, such as the H-bond, proton transfer, charge transfer, van der Waals force and so on. In addition, ESR analysis found that covalent bond exists between humic acid and 2,4-D or its degradation product during the process of adsorption.