O-o' methylene bridge is one of primary linkage among phenol-formaldehyde resins structure units. Pyrolysis mechanism of the 2BHM as a model compound was investigated by using density functional theory B3LYP methods at 6-311G(d,p) level in Gaussian 09 package. Six kinds of paths of pyrolysis reactions were designed, and the equilibrium geometries of the reactants, transition states and products of every reaction path were optimized, and the transition states were checked using IRC method. The standard kinetics parameters of every path were calculated. The calculation results show that Path3 are the major reaction channels and the corresponding products are phenol and o-cresol. Product of all path include phenol, and the CO₂ generates more easily than CO. Pyrolysis experiment results show that phenol content is the highest, and no CO is formed. This shows that the calculation results are basically identical to the experimental results, at the same time also shows that the application of quantum chemistry calculation theory to study the pyrolysis mechanism of phenolic resin is a kind of effective research method.