<p>To investigate the influence of CO₂ on the co-pyrolysis characteristics of sewage sludge and poplar sawdust, a 1:1 (w/w) blend of sewage sludge and poplar sawdust was employed as the experimental material. Pyrolysis experiments were performed in a fixed-bed reactor under both CO₂ and N₂ atmospheres across a temperature range of 500–800 ℃. The influence of CO₂ atmosphere on the composition of pyrolysis gas and tar was examined. The results show that increasing temperature decreases the char yield, while increasing the yields of CO, CH₄, and H₂. In comparison to N₂, a CO₂ atmosphere promotes the generation of CH₄ and CO, while suppressing the formation of H₂. CO₂ atmosphere influence on the composition of tar. The maximum tar yield and the highest total peak area corresponding to phenolic compounds were observed at 500 ℃ under CO₂, whereas these values were recorded at 600 ℃ under N₂. Increasing the temperature within CO₂ facilitates the formation of aromatic hydrocarbons in tar. The content of oxygen-containing compounds exhibits an initial decline followed by a subsequent increase.</p>