Abstract For a fixed bed gasifier, coal gas is mainly derived from dry distillation zone and gasification zone. The upstream gas from gasification zone will inevitably affect the composition and production of dry distillation gas. Therefore, the composition of upstream gas and the reaction conditions of dry distillation zone were simulated to perform experiments of Yining coal pyrolysis under a series of atmospheres. Some new discoveries are obtained. H2O and the hydrogen-containing gas have a significant impact on the release of dry distillation gas. H2O inhibits the release of CO, CO2 and CH4, but promotes the release of H2 which is not from char−H2O gasification. When the hydrogen-containing gas passes through dry distillation zone, the path of stabilizing radicals is completely changed, resulting in that coal pyrolysis changes from a process of generating H2 under inert atmosphere to a process of consuming a large amount of H2. In addition, water gas shift reaction is the only homogeneous reaction observed obviously in dry distillation zone, which can promote the production increase of CO2, but can not prevent the production decrease of H2 in coal gas.