Using KMnO4 and MnSO4·H2O as raw materials, active manganese dioxide was prepared at room temperature and pressure and hydrothermal condition. The synthesized active manganese dioxide was characterized by XRD, TEM and N2 adsorption-desorption, respectively. The effects of different preparation methods on structure and adsorption performance of the synthesized products were investigated. The results show that the reaction temperature and pressure have a great effect on the morphology and adsorption performance of active manganese dioxide. The shapes of active manganese dioxide prepared at room temperature and pressure are all rod. The products synthesized by hydrothermal method are mesoporous fibers and have better adsorption performance. The adsorption behavior of 2,4-dinitrophenol on active manganese dioxide is well described by Langmuir isotherm equation (R2>0.99) and pseudo-second-order kinetic equation (R2>0.99), which indicate that the adsorption process is monolayer and chemical adsorption. The pH value of solution has a significant effect on the adsorption of 2,4-dinitrophenol on active manganese dioxide, and the maximum adsoption capacity is 2.539 mg/g at pH=7.