Abstract: Experimental studies on co-pyrolysis of coal and lignin are carried out on a fixed-bed reactor to investigate composition and transformation of the co-pyrolysis products. The results show that co-pyrolysis reduces yield of char and promotes yield of gas, the maximum pyrolysis gas yield increases by 33.1%. Co-pyrolysis has a significant promotion effect on generation of CH₄ and CO. The interaction between the pyrolyzed volatile fractions of coal and lignin shows the most pronounced interaction at a coal to lignin mixing ratio of 1∶1, and the pyrolysis tar yield shows a positive synergistic effect. Guaiacols are converted to monophenols and bisphenols during the co-pyrolysis process. Content of monophenols and bisphenols increase by 2.9% and 9.8%, respectively, while content of guaiacols decreases by 5.1% compared with the theoretically calculated values. The breakage of carbonyl and carboxyl groups, and the interaction with volatile components are enhanced, which inhibits formation of ethers, aldehydes and acids, and promotes generation of phenols, release of oxygenated gases and stabilization of pyrolysis tar. The introduction of lignin into coal pyrolysis also significantly promotes the upgrading of tar in which light components is nearly 90%.