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This article investigated the interaction mechanism between carbon monoxide (CO) and lignite organic matter in lignite liquefaction systems. The study found that a CO atmosphere can facilitate lignite conversion, but its hydrogen supply capacity is poor, resulting in lower liquefaction effects compared to an H 2 atmosphere. Increasing the initial reaction pressure and CO content can enhance the conversion of lignite to low molecular compounds. In-situ studies on lignite pyrolysis in CO and N 2 atmospheres show that CO plays an effective role in promoting the fracture of multiple hydrogen bonds present in lignite, which is linked to the water-gas shift reaction that CO takes part. Additionally, CO can also facilitate the breaking of oxygen-containing ether bonds in lignite, thereby eliminating oxygen and producing CO 2 in the gaseous phase. Density functional theory (DFT) calculations demonstrate that CO reacts with the group after the ether bond breaks, which reduces the formation energy of the product and promotes the ether bond breaking. In summary, CO in syngas may benefit the breaking of ether and hydrogen bonds in lignite during liquefaction, thus promoting lignite conversion. [Display omitted] • The interaction mechanism between CO and lignite organic matter in liquefaction was studied. • CO in syngas may be beneficial to the breaking of ether bond and hydrogen bond in lignite. • CO can promote the conversion of lignite to low molecular compounds during liquefaction. [ABSTRACT FROM AUTHOR]