Abstract: The homolytic bond dissociation energies (BDEs) of C_α-O and C_β-O bonds in 27 lignin trimer model compounds were calculated by employing density functional theory methods at M062X level with 6-31++G (d, p) basis set; the effects of various substituent groups (CH₃, CH₂OH and OCH₃) at different positions on the BDEs of C_α-O and C_β-O bonds were investigated. The results indicated that a single methoxyl group at R₂ or R₃ has a minor influence on the BDE of C_β-O bond, whereas two methoxyl groups at R₂ and R₃ lead to an obvious decrease in the BDE of C_β-O bond. The decrement in the BDE of C_β-O bond from the methoxyl groups at R₂ and R₃ can be enhanced by the methoxyl groups at R₄ and R₅, but is hardly influenced by the substituent groups at R₁. Meanwhile, the BDE of C_α-O bond is gradually reduced when the H atoms at R₄ and R₅ are successively substituted with methoxyl groups; the decrement in the BDE of C_α-O bond from the methoxyl groups at R₄ and R₅ can be strengthened by the methoxyl groups at R₂ and R₃. Furthermore, the methyl and hydroxymethyl groups at R₁ can gradually increase the BDE of C_α-O bond and this effect is weakened when the H atoms at R₂ and R₃ are successively substituted with methoxyl groups. The methyl group at R₁ has little influence on the BDE of C_β-O bond, which is however dramatically increased by the hydroxymethyl group at R₁.