A self-made directional solidification device was used to fabricate d 80 mm high purity aluminum ingots. SEM and AFM were used to detect the shape of grain boundaries. The orientation of the grain was studied by X-ray diffractometry. The results show that the nucleation points locate at the intersections of three adjacent grains. The lattice orientation of grains does not alter in the horizontal direction, but gradually approaches the optimum growth direction in the vertical direction during the growth process. All the grains suffer the competition and only the one whose orientation is closest to the preferred direction can occupy the final growth space.