Abstract: Performances of alumina prepared by pyrolysis aluminium chloride which was a key technology in a new acid process (the doublecycle method) were studied by the chemical analysis and Xray diffraction (XRD). The pyrolysis properties of crystalline aluminium chloride at the static atmosphere and water vapor status with different temperatures and time were mainly investigated. By comparison， the results showed that the decomposition rate in water vapor was significantly higher than that of the direct decomposition one without water vapor. Chlorine mass fraction in the product could be reduced to 014% with the optimal conditions for the pyrolysis in water vapor of a pyrolysis temperature of 800℃ and a pyrolysis time of 30 minutes. while for that in the static atmosphere， the chlorine mass fraction of 025% was obtained at a pyrolysis temperature of 900℃ for holding a pyrolysis time of 60minutes.

Key words: aluminium chloride, pyrolysis, phase analysis, alumina, chemical analysis