Plant activities might alter the environmental behavior of organic pollutants in rhizosphere soil during phytoremediation. To further illustrate the mechanisms underlying the varying adsorption about the different adsorbing abilities of rhizosphere soil (RS) and non-rhizosphere soil (NRS) for the same pollutant, atrazine was selected to investigate the adsorption traits in the NRS and RS of Pennisetum americanum (L.) K. Schum (P. americanum), a potential phytoremediator of atrazine pollution. Furthermore, the different fluorescence spectral properties of the dissolved organic matter (DOM) extracted from RS and NRS when binding with atrazine were also investigated. RS exhibited a higher atrazine adsorption capacity than NRS, although the kinetic and isothermal properties of atrazine adsorption onto the two kinds soil were described by a pseudo second-order model and the Freundlich model. The DOM extracted from RS showed a stronger atrazine-binding ability than that extracted from NRS, as proven by the much more obvious decrease in fluorescence intensity when binding with atrazine. Although synchronous fluorescence spectra analysis suggested that both DOM types bind atrazine using a static fluorescence quenching mechanism, Fourier transform infrared spectroscopy showed that some distinct functional groups, which might liable to combine with atrazine, were found in only the DOM extracted from RS. Considering the findings mentioned above and the fact that the typical chemical characteristics of RS were different from those of NRS, we concluded that the P. americanum enhances the atrazine adsorption ability of RS by regulating the chemical characteristics and atrazine-binding ability of DOM in RS.