Abstract: The oxidation characteristics and mechanism of aluminum cluster in different oxidizers were studied. ReaxFF force field was used to simulate the initial oxidation process of Al-O₂ system and Al-H₂O system respectively. Results show that in Al-O₂ system, the temperature of environment decides on whether there exists Al atom around aluminum cluster during initial oxidation. Moreover, there exists a temperature threshold value, below that the Al atom does not exist. For Al-H₂O system, the influences of the number of initial water molecules and the temperature were studied. Studies show that water tends to promote the dissociation of water molecules absorbed by aluminum cluster. Reaction mechanism of aluminum cluster(2 nm) and water molecule were also discussed and compared with that of Al_n(n=3～20)cluster and water. The results show that there exists evidence difference in the reaction mechanism when the number of initial water molecule and temperature are distinct.