Totrefaction of Eupaturium adenophorum Spreng., a major invasive plant in southeast China, was investigated in a laboratory fixed bed at temperatures of 200-325 degrees C and residence time of 30 min for improving the properties of the biomass as fuel. During torrefaction, a large amount of oxygen was removed from biomass, which made the torrefied biomass more like,coal. Oxygen in torrefaction products was characterized to study the quantity and approach of oxygen migration. In gas products, oxygen existed as CO2 and CO, and-in the liquid product, it existed in forms of H2O and oxygen-containing compounds, such as acids, alcohols, aldehydes, ketones, furans, guaiacols, phenols, and extracts. The oxygen in the solid product presented as oxygen-containing functional groups, of which the proportion of C-OH and C-O-C obviously decreased with the increase in the torrefaction temperature. At low temperatures (200-250 degrees C), oxygen in biomass was transferred to H2O with traces of oxygen migrated to bio-oil. As the torrefaction temperature increased, a growing amount of oxygen in biomass migrated to bio-oil and gas but dehydration still dominated deoxidation. Carbon migration coupled with oxygen migration led to energy loss to decrease the energy yield of the torrefied product or the obtained fuel. From the perspective of deoxidation effectiveness and carbon loss during torrefaction; 250 degrees C was suggested to be the optimal temperature for torrefaction of E. adenophorum Spreng.