Abstract: Al₂ O₃ thin films were prepared on Si wafers and glass substrates by atomic layer deposition.SEM and XRD,XPS,ellipsometry,UV-visible spectrophotometer and HP4284 A precision LCR tester were used on the surface morphology,microstructure,composition,thickness,optical properties and electrical properties of Al₂ O₃ thin film were analyzed. The main conclusions were as follows : the surface roughness of the Al₂ O₃ thin film decreases with the increase of deposition temperature and increases with the increase of Trimethyl Aluminum （TMA） pulse time,and has a high transmittance in the visible region. The excellent properties were obtained when the deposition temperature was 300 ℃ and the pulse time of TMA was 0.1 s.