Abstract: In order to study the secondary oxidation characteristics and the critical temperature range of brown coal treated at different temperature and time. The Yunnan brown coal was pretreated by 60 min to 120 min oxidation at 100 ℃ to 175 ℃, and then its spontaneous combustion characteristics are tested. At the same time, the treated coal samples were analyzed by Thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy. The result shows that: the spontaneous combustion characteristics of the pre-oxidized coal sample are enhanced, and the oxidation of H₂O₂ heats up to 90 ℃ with a minimum of 15 min. The oxygen functional groups in coal samples increase and the surface structure is loose. The variation of the spontaneous combustion characteristics of the secondary oxidation coal sample is affected by the two factors of the pre-oxidation temperature and time, showing a tendency to increase first and then decrease. After treatment with 120 min, the apparent activation energy of coal sample at 200 ℃ to 400 ℃ is 66.530 kJ/mol to 68.985 kJ/mol.