Abstract: With the free radical reaction during the pyrolysis process of heavy organics as the background, the research approach based on density functional theory was adopted to exploring the induction of free radicals on covalent bond and its effect on covalent bond dissociation energy. The energies of seven kinds of covalent bond reactions induced respectively by ·CH₃, ·OH and ·H were calculated theoretically on the Gaussian 09 program at the level of ωB97XD/6-31G**. The results indicate that the steric hindrance effect plays a significant role in the energy barrier of free radical induced reaction, while the influence of the covalent bond type plays a minor role. When the isogroup induced exchange reaction of ·OH and ·H does not proceed, the induced energy barrier of ·OH is about 40 kJ/mol higher than that of ·H and the induced energy barrier of ·CH₃ is about 50 and 90 kJ/mol higher than that of ·OH and ·H respectively. When the isogroup induced exchange reaction of ·OH and ·H works, it will result in the increasing of 70 kJ/mol of the energy barrier. During the process of calculation, the specific situation of induced reaction should be judged and revised. The above values can be used to estimate the energy barriers of different covalent bond induced reactions.