Hangjin2^# clay is a layered iron-bearing natural mineral found in Ordos, Inner Mongolia. In succession, X-ray diffraction, pyridine adsorption Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize Hangjin2^# clay. X-ray photoelectron spectroscopy results indicated that Fe in Hangjin2^# clay skeleton structure mainly exists as Fe(Ⅲ) and Fe(Ⅱ). Moreover, the binding energy of Si and Al in Hangjin2^# clay has increased significantly compared with the standard binding energy of Si and Al in silicon-oxygen tetrahedron and octahedron aluminum oxygen, which indicated the presence of Lewis and Brönsted acid sites. In heterogeneous Fenton reaction, structural iron in Hangjin2^# clay could react with H₂O₂ to produce?OH to degrade methyl orange, but the rate is slow and difficult to cycle. After acid activation, Si and Al’s increased binding energy in activated Hangjin2^# clay has been confirmed, and iron in activated Hangjin2^# clay has transformed into non-structural iron which coexists in the form of Fe²⁺ and Fe³⁺. Whatsmore, the increase Lewis acid and Brönsted acid sites on activated Hangjin2^# clay surface have been confirmed by the characterization of X-ray photoelectron spectroscopy, pyridine infrared, and ammonia temperature-programmed desorption. After activation, Fe³⁺ and Fe²⁺ could circularly react with H₂O₂ to continuously generate ·OH to degrade methyl orange. Furthermore, Brönsted acid sites on the activated Hangjin2^# clay surface could provide protons to surround H₂O₂, and the formation reaction of $HO_{2}^{-}$ will be inhibited. Lewis acid sites on activated Hangjin2^# clay surface could increase adsorption oxygen content. Moreover, Fe²⁺ can be oxidized by adsorption oxygen to form Fe³⁺, promoting the circulation between Fe²⁺/Fe³⁺. Furthermore, in the oxidation process, the electron could transfer to adsorption oxygen to form $O_{2}^{·-}$ which can be reacted with protons provided by Brönsted acid sites to form ·OH. These ·OH and $O_{2}^{·-}$ are oxidizing radicals, which could improve the reaction activity of Hangjin2^# clay in heterogeneous Fenton reactions. In addition, X-ray diffraction analysis indicated that acid activation could convert $CO_{3}^{2-}$ to $SO_{4}^{2-}$, while $SO_{4}^{2-}$ has a less negative effect on Fenton reaction compared with $CO_{3}^{2-}$.