In this study, we employed pyrolysis behavior and kinetics by Flynn-Wall-Ozawa method and Friedman method to analysis the thermostability of the MnFe2O4 nanoparticles/poplar wood composite, and analyzed the change of different proportion of MnFe2O4 in these composites for the thermostability by contrasting activation energy between the different samples. The pyrolysis processes of these composites were comprehensively investigated at different heating rates (10, 20, 30 and 40 °C/min-1) and pyrolysis temperatures of 600 °C in N2 and air atmosphere. These results indicated the thermostability of composites improved as the proportion of the MnFe2O4 nanoparticles increased. And the structure analyses of these composites from the microscopic view point of nanoparticles were applied to analysis the reason of thermostability enhancement of the poplar wood after coating MnFe2O4 nanoparticles. Additionally, due to its high initial oxidative decomposition temperature under air atmosphere, this composite and its preparation method might have high application potential, such as flameresistant material and wood security storage. This method also could provide a reference for other biomass materials. Synthesized MnFe2O4/C composite under the guidance of pyrolysis behaviors and kinetic study in N2 atmosphere exhibited good adsorption capacity (84.18 mg/g) for removing methylene blue dye in aqueous solution and easy separation characteristic.