To investigate the mineral behavior of lignite ashes under gasification conditions, 450 ℃Xiaolongtan lignite ash samples (XLT-LTA) treated at different temperatures or pressures under reducing atmosphere (H2/CO2=1 : 1, volume ratio) have been examined by means of an SC-444 apparatus, a scanning electron microscope with an energy dispersive X-ray detector (SEM-EDX), and by X-ray diffraction (XRD). The results showed the sulfur content in the XLT-LTA to be much higher than that in ashes prepared at 815 ℃, as a result of the release of sulfur dioxide during the oxidization of pyrite. With increasing temperature, the XLT-LTA particles gradually agglomerate and form partially molten surface entities with obvious apertures, and the content of iron and calcium in the congeries or molten parts increases due to the fusion of fine ash particles with the enrichment of iron and the formation of low-temperature eutectics of calcium and iron. An increase of pressure restrains the decomposition of calcite and muscovite, and promotes the formation of iron minerals (e.g., hercynite, cordierite, and sekaninaite) and orthoclase. The content of amorphous material also increases with increasing pressure.