The experimental method for studying interface atomic structure between amorphous layer and crystal by MeV ion scattering and channeling is described. This method is applied . to study the Al2O3/Al(100) interface. Thin Al oxide film are formed on clean Al(l00) surface in pure oxygen ambience at 400℃. The experimental results show that the composition of the oxide film is precisely Al2O3, and the interface between Al oxide film and Al(l00) bulk is very sharp, the reconstructive layer under the Al2O3 film is no more than one monolayer. Monte carlo simulations indicate the distance between displaced Al atoms on the reconstuctive layer and Al〈l00〉axis is 0.18 A. At room temperature, the oxygen adsorption layer of Al〈l00〉 is primarily stoichiometric A1O at low surface coverages.