Abstract: The experimental study of ultrafine aluminum oxide formed by the mixture detonation of aluminum nitrate and PETN used to maintain steady detonation is presented. The detonation product without any disposal is analysed by TEM、XRD、DTA/TGA and BET. The results show that the detonation product is ultrafine and globose aluminum oxide, the range of granularity is from 10~50 nm, the average size is 25 nm. The aluminum oxide is aluminum oxide. Based on the experimental results, we concluded that the ultrafine aluminum oxide directly agglomerated each other with the ion or molecule formed in the reaction area of detonation. Because the process of agglomeration and growth completed in the microsecond range, the grains did not grow towards the favored direction and took spherial form.