Aluminum-doped Zinc Oxide (ZnO:Al, AZO) thin films are deposited on K9 glasses by the DC magnetron sputtering. The deposited samples are annealed under the condition of vacuum and 300℃. Effects of annealing time on the microstructure, surface topography and optical properties of AZO thin films are researched, respectively. Results show that the optimal annealing time is 2 h. AZO thin films deposited under this condition has a stronger (002) diffracting peak with the grain size of 17.2 nm, and the surface microstructure is smooth and compact. The average transmittance of the sample in the UV-Vis band is 93.47%, and the corresponding optical energy gap is 3.41 eV.