The geometrical structure of Cu doped 32-atom supercell of AlN was optimized by using the ultra-soft pseudopotential method of total-energy plane wave based on density functional theory （DFT） . Density of states，band structure and optical properties were calculated and discussed in detail. The results revealed that The Cu dopants were found spinpolarized. Band structures show a half metallic behaviour. The band gap of Cu-doped AlN reduced and the absorption ability to infrared visible light strengthened obviously,the loss of energy decrease The ferromagnetic ground state in Cu-doped AlN can be explained in terms of p-d hybridization mechanism. These results suggest that Cu-doped AlN may present a promising dilute magnetic semiconductor.