The electronic structure and optical properties of ZnO are calculated in different Al doping. The effects of Al doping on the crystal structure, band structure, density of state and optical properties are analysed by using the first-principles calculation of plane wave ultra-soft pseudo-potential technology based on density function theory(DFT). The calculated results reveal that there are lots of carriers in the bottom of conduction bands due to the donor doping, which improve greatly the conductivity of the Al-doped system, and the Fermi level moves into conduction bands(CBs). Moreover, the optical band gap is broadened and moves towards lower energy. The optical transmittance of Al doped AZO is as high as 85% in the visible region, the UV absorption edge is blue shifted greatly with increasing Al doping concentration. All calculated results showe that the AZO materials can be used as excellent transparent conducting films.