Abstract: Globular nanometer γ aluminum oxide powder was synthesized through detonation of aluminum nitrate.The experimental powder samples were heated from room temperature to 600℃、800℃、900℃、1000℃、1100℃ and 1300℃ respectively for sintering,and then were analysed by means of XRD to investigate the crystal granularity of the powder samples sintered at different temperature.The curves of XRD manifested that with the sintering temperature rising,the aluminum oxide changed from γ to δ,then to θ,and then to α and the grain of the nanometer aluminum oxide was refined.The most grain refinement appeared at 800~1000℃.