Al doped ZnO thin films were prepared on glass slide substrates by magnetron sputtering. The effects of different argon oxygen ratios, the annealing temperature, the annealing ambient and Al content on the structure have been investigated systematically. The results show that all films can be indexed as ZnO hexagonal structure, and the processing parameters play an important role in the microstructures. Moreover, the film deposited at argon oxygen ratio of 6∶1and annealed in vacuum at 500℃ shows good crystallization with preferred growth (002) direction.