Abstract: The effect of Fe on structure of unreacted residues from combustion of demineralized Shengli lignite at ignition temperature was studied. TGA was adopted to investigate the ignition temperature of demineralized and Fe adding lignite, which were combusted at ignition temperature in quartz tube reactor to attain solid unreacted residues. The structure properties of lignite and the unreacted residues were investigated by FT-IR, XPS, XRD, and Raman spectra to study influence of Fe on the combustion reaction. The results indicate that adding of Fe lowers the ignition temperature of demineralized Shengli lignite, especially when the adding amount was 3.50%. The FT-IR of solid unreacted residues demonstrates that the adding of Fe has no obvious effect on functional groups of unreacted residues, suggesting that the functional groups are not the main factors to affect he combustion performance. The Fe adding accelerates the decrease of carbon-oxygen structure of SL⁺ during combustion and causes the reduced aromaticity and graphitization degree of unreacted residues, and favors the increase in alkyl side chain and crystal structure defects, indicating that the Fe adding promotes the changes in carbon-oxygen structure during combustion and restrains graphitized transformation of unreacted residues.