Abstract: In order to study the action mechanism and the principle of active phase regulation on coal liquefaction cata- lyst,the phase transition process of Fe2 O3 in coal liquefaction had been investigated. The study was performed using X-ray powder diffractometer (XRD),saturate magnetization and scanning electron microscope (SEM). The Fe2 O3 was identified and there was no FeS2 because S element was insufficient in the system. Due to the sufficient H element,the Fe2 O3 had been reduced to Fe3 O4 . The temperature experiment results showed that Fe2 O3 was vulcanized into two crys- tal forms of Fe7 S8(monoclinic and trigonal system) at 400 ℃ ,and the Fe7 S8 was desulfurized into Fe9 S10 and Fe0. 95 S. The pyrrhotite was desulfurized to FeS continuously when temperature risen to 420 ℃ and 440 ℃ . The time experi- ment results showed that the velocity of Fe7 S8 transformed to Fe9 S10 was slower than Fe9 S10 decomposition in the sys- tem when the reaction time was 0 min at 420 ℃ . Fe7 S8 decomposed to produce lower S / Fe pyrrhotites at a uniform speed when the reactions continue. More stable FeS was generated when the reaction time was 90 min. The asphaltene yield increased because catalyst capacity decreased. The SEM photos showed that there were long strip of macromolec- ular condensation polymers in the system. The atmosphere experiments showed that the same kind of iron sulfide was generated in nitrogen and hydrogen,but Fe7 S8 generated in nitrogen was less than in hydrogen