The work function and surface energy of aluminum with different orientations are investigated by employing the DFT simulation. We mainly focus on two situations: pure aluminum surface and aluminum surface with impurities. The numerical results indicate that the work function of Al (100) is larger than Al (110). With the introduction of the impurities (carbon atoms), the work function increases because of the extra electric dipoles on the surface. We also find that the surface energy of Al (100) is smaller than that of Al (110) indicating that Al (100) surface is more stable. When there are impurities on the surface, the surface energy decreases for silicon impurity and increases for calcium impurity. The magnitude of the increase is related to the orientation of the surface.