In a similar range of Al-2N doping amount to that in the present paper, the absorption spectra of ZnO doped system and two kinds of experimental results have been reported in the literature. However, there is no reasonable explanation for the absorption spectra of ZnO doped system. In order to solve the problem, all calculations in the present paper are carried out by the CASTEP tool in the Materials Studio software based on the first principal ultrasoft pseudopotential of the density functional theory, and the geometric structures of ZnO, Zn0.98148Al0.01852O0.96296N0.03704 and Zn0.96875Al0.03125O0.9375N0.0625 systems are constructed by first-principal. All the models are based on the optimization of the geometry structure. And the distribution of the band structure, the density of states and the absorption spectra of the doping system are calculated by the method of GGA+U. The results indicate that in the range of the doping content restricted in the present paper, the bigger the doping amount of Al-2N, the smaller the volume of doped system is; the higher the total energy, the more the stability decreases; the higher the formation energy, the harder the doping becomes and the narrower the optical band gap of doped system. Meanwhile, the higher the Al-2N doping content, the narrower the optical bandgap of the doping system becomes, which suggests that the more significant the red shift of absorption spectrum of Al-2N doped ZnO system is. Therefore, the doped system is controlled within the doping content in experiment to obtain the narrow optical band gap and red shift in absorption spectrum in Al-2N doped ZnO, in addition to the control of lower nanoscale of Al-2N doped in ZnO. At the same time, all doping systems are p-type degenerated semiconductors. Then, the higher the Al-2N doping content, the smaller the relative concentration of free holes of doped system is; the smaller the hole effective mass, the lower the mobility is; the lower the hole conductivity, the worse the conductive property of doping system is. The calculated results are in agreement with the experimental results. The research shows that Al-2N co-doped ZnO can be a new type of semiconductor material, a functional material which is used at low temperature end of thermoelectric power generation.