In this study, a sealable fixed‐bed reactor was developed to investigate the influence of gaseous products on lignin pyrolysis with a strategy of hydrogen self‐supply, and lignin pyrolysis performances at various temperatures were monitored by the comprehensive characterization of the generated products, including gas, bio‐oil and char. The results showed that the release of volatiles (both gas and bio‐oil) from lignin was strengthened in this sealable system when the temperature rose, and therefore less char was left. Meanwhile no H2 was detected under any of the operating conditions, which is a common component in pyrolysis gas from conventional reactors, indicating its participation in lignin pyrolysis. Furthermore, the formation of CO and CO2 in the employed pyrolyzer benefited from not only the thermal evolution of feedstock, but also the interactions between char residues and generated gas components. Meanwhile, because of the hydrogen self‐supply, compounds in bio‐oil were enriched and only nine species were detected, which were all phenolic compounds. Vanillic acid was dominant, and its relative content was up to 38.86% for Alcell organosolv lignin and 34.41% for soda alkali lignin. This illustrates that highly selective production of phenolic compounds from lignin pyrolysis can be achieved by self‐supplying hydrogen from pyrolysis gas.