During the manufacturing of Al-based thin films for electronic applications, a post-deposition annealing is required in order to achieve a lower resistivity. However, the electrical transportation behavior of the magnetron sputtering Al film has been rarely investigated. To address this objective, we have explored the microstructure of the film before and after annealing with emphasis on the structural features related to diffusion and interface using TEM observation. Hall-effect measurement was employed to determine the variation of carrier density and mobility brought by the evolution originating at the interface. The results demonstrate that during annealing an intimate contact was formed between the film and substrate via diffusion, leading to a combination of high mobility and high density. Furthermore, a model was proposed from the aspect of energy bands in order to explain the positive effect of the interface phenomenon upon electron conductivity.