Abstract: Fast pyrolysis of Huolinhe lignite was carried out under pressure in a tubular reactor, and the CH₄ evolution at CO atmosphere was examined. CO dissociation state O(a) adsorbed on coal is an active center. The stronger electronegative O could induce the electron cloud of other atoms around O(a) atom to offset to it, which could weaken the strength of original chemical bonds and promote their breaking. These result in the cracks of the aromatic ring, side chain, ether linkages and aliphatic chain in the char, which could produce more free radicals. The free radicals could stabilize the fragments produced in the pyrolysis, and lead to more CH₄ generated and involved. Therefore, the CH₄ yield is higher under CO than it in N₂. The CH₄ yield increases by 12.5% under CO compared with N₂ at 900 ℃ and 1.0 MPa. The CH₄ yield increases with raise of temperature and pressure.