The energy change generated from aliphatic sulfoether structure (C₆H₅CH₂SCH₃) in coal adsorbing O₂ and oxidation was studied by using Gaussian 03 program and density functional theory (DFT) method at the B3LYP/6-31G (d, p) level, and the oxidation mechanism was analyzed to provide theoretical basis for preventing coal spontaneous combustion. The results show that the energy of complex Ⅰ formed from C₆H₅CH₂SCH₃ structure in coal adsorbing O₂ is the local least, and the formation is a stable no barrier process in thermodynamics. The interaction distance d_S-O between C₆H₅CH₂SCH₃ structure in coal and O₂ is 2.582 Å, and the interaction energy is -20.60 kJ/mol after CP correction. Analyzing the electron density change of complex Ⅰ shows the interaction is Van der Waals forces, which belongs to physical adsorption. The complex Ⅰ will react when it absorbs enough energy. There are five reaction paths in oxidation reaction of C₆H₅CH₂SCH₃ structures in coal, Path 4 is the main reaction path, and P₃ (C₆H₅CH₂SOH+CH₂O) is its principal product. The analysis shows that C₆H₅CH₂SCH₃ structure in coal is easy to be preliminarily oxidized, only 12.36 kJ/mol energy is needed and the energy of physically absorbing an O₂ molecule is enough. But deep oxidation along with Path 4 needs as much as the energy of physically adsorbing 5 O₂ molecules.