By means of chemical analysis, TG DSC, FT IR, XRD, SEM/EDS and optical microscopy, the chemical composition and mineral phases of fly ash from LIFAC sulphur removal process in Nanjing Xiaguan Power Plant were studied. These of ordinary fly ash were also studied as comparison. The results show that except for glass phase and crystals identical to the ordinary fly ash, active free CaO, Ca(OH) 2,CaSO 4,CaSO 3 and CaCO 3 remainder are detected in LIFAC fly ash.