The geometry structure, electronic structure, total energy, Mulliken changes of He atom in the Al octahedral site and tetrahedral site were studied by first-principle plane-wave pseudopotential method and GGA. The calculation results indicated that the crystal lattice of Al was changed when He atom enter to the interstitial of Al, but the total results are the change of crystal lattice in octahedral site smaller than tetrahedral site. For Al system, the impurity formation energies of helium atom are 1.3367 and 2.4411 eV in the octahedral site and tetrahedral site, respectively. It is found that for He atom the best stable state is octahedral of Al. At the same time, the site occupancy and its effect of He atom in crystal cell was analysis in this article, and the effects of helium atom in Al system on band structure and density of states and valence electron density are discussed.