First-principles theory is adopted to analyze the characteristics of defects in ZnTe induced by In doping. The geometry structures, formation energies, band structures, densities of states and transition levels of the defects are calculated. The results show that there are two kinds of major defects in In-doped ZnTe. One is the atomic substitution defect of Zn replaced by In, which gives rise to a transition level located at 2.6 eV beneath the conduction band. The other is a complex defect, consisting of one In substituting Zn and one nearby Zn vacancy, which results in a transition level 0.33 eV higher than the top level of valance band. Electron transition between these two transition levels can be regards as the origin of the near-infrared light observed experimentally in In-doped ZnTe.