Oxidation of aluminum was studied by first principle density functional theory (DFT) calculations. The total energy calculations for bulk aluminum, surface of Al(001) and O(4x2)/Al(001) were carried out using pseudopotential plane-wave method. Car-Parrinello molecular dynamics (CPMD) simulations were performed for the clean surface of AI(001) and molecule oxygen adsorption on AI(001). The calculated equilibrium lattice parameter, bulk modulus, total energy per atom and the chemical potential were in good agreement with experimental results and other DFT works. The electronic charge density studies showed that almost all the valence electrons of the topmost At atoms had transferred to the adsorbed oxygen atom. CPMD simulations for molecule oxygen absorbed Al(001) showed two stage reactions. In the first stage, structural relaxation occurred, molecule oxygen as a whole moved down onto the aluminum surface, accompanied by an increased temperature. In the second stage, ions achieved even higher temperature and then cooled down to initial values with a large temperature fluctuation. Meanwhile, dissociation of the oxygen molecule was exhibited. No evidence was found to indicate that the dissociation of an oxygen molecule and chemical adsorption of atomic oxygen took place in separate stages.