This study mainly researched the adsorption properties and adsorption mechanism of atrazine on three different types of humic acids: the black soil humic acid, the chestnut soil humic acid and the humic acid purchased. 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 atrazine and humic acid. The results showed that the sorption of humic acid on atazine was very fast at the beginning, then went to slower and finally came to equilibrium. The relationship between the amount of atrazine sorbed by the three humic acids and reaction time all fitted logarithmic and hyperbolic equations well. Adsorption isotherms of atrazine on the three humic acids all are L-type and in accordance with the linear model and the Freundlich model. Because of the different structure, there is significant difference between the adsorption isotherm of atrazine on purchased humic acid and extract humic acid. The interactions between humic acid and atrazine are mostly weak forces, such as the H-bond, proton transfer, charge transfer, van der Waals force and so on. In addition, ESR analysis proved that charge transfer exists between humic acid and atrazine during the process of adsorption.