Abstract: The influence of hydrotreating temperature on the inferior FCC diesel oil was investigated at 12.0 MPa, volume space velocity of 0.5 h-1 and hydrogen to oil volume ratio of 800 in a three 300mL hydrogenation fixed bed in series. Raw material oil and the hydrotreated diesel oil were cut into narrow fractions, and the variation of hydrocarbon group compositions of the narrow fractions with distillation range was studied. The results show that at the optimum hydrotreating temperature of 370 ℃, the density of hydrotreated diesel is 0.865 1 g/cm3，the sulfur and the total aromatics content are 27.51 μg/g and 12.8%, respectively and the cetane index increases 15 points. Over 92% of bicyclic and tricyclic aromatic hydrocarbon of every narrow fraction is removed. It is found that most of single-ring aromatics and tricyclic naphthenic is concentrated in 285~350 ℃fraction range, which is required further hydro-upgrading to reduce the density and improve cetane number of inferior diesel oil.