Abstract: Direct coal liquefaction reactivity under sulfur’s effect was studied via L₉（3⁴） orthogonal experimental design. Pressure, temperature, H₂S volume content in H₂S/H₂, and S/Fe mole ratio were considered as factors while coal conversion, oil yield, sulfur content of oil, and hydrogen consumption ratio as the target indexes. The sulfur migration mechanism in the reaction was also proposed. The results showed that the temperature has a remarkable effect on oil yield. When the temperature increases from 420 to 470 ℃, there’s an average increase of 19.0% in oil yield. H₂S plays three roles: decreasing hydrogen consumption ratio, improving light product （including oil and gas） generation, and increasing sulfur content of oil. There is a decrease of 0.3% hydrogen consumption ratio and an increase of 0.9% sulfur content of oil when H₂S content is increased from 0−1%. S/Fe molar ratio within the reasonable range can promote oil yield, and higher oil yield was obtained at the S/Fe ratio of 0.8 compared with that at S/Fe being 1.0 or 0. During the processing of DCL, elemental sulfur migrates to THFI mostly, and there’s an extra 2% sulfur content of THFI if only elemental sulfur is added in the reaction system. Based on the results of the orthogonal experiment, the liquefaction experiments under different S/Fe molar ratios in pure hydrogen atmosphere, and different H₂S volume content under constant 0.4 S/Fe molar ratio were further studied. From the distribution of sulfur in oil and asphaltene, combined with the changes in functional groups and free radical concentration, the effect mechanism of H₂S and elemental sulfur and the migration rule of sulfur in coal liquefaction reaction were deduced. It was indicated that the free radical concentration of THFI is related with oil yield and hydrogen consumption to some extent. Oil yield shows a peak value at S/Fe atomic ratio being 1.2 while the free radical concentration of THFI gets its minimal value. At 0.25% H₂S content, the hydrogen consumption rises apparently while the free radical concentration of THFI reaches bottom peak. It seems to be easier for H₂S than elemental sulfur to react with the precursor of light products, and promote conversion of heavy fraction to the light products. Only in excessive amounts can elemental sulfur combine with asphaltenes slightly. The roles of H₂S and elemental sulfur promote hydrogen supply in the gas phase, but have no obvious effect on the functional groups of asphaltene.