Abstract: The defect forming energy, transition level and carrier nonradiative recombination coefficient of Mn and Sn doped α-CsPbI₃ system are investigated by first-principles based on density functional theory. It is found that the lattice constant of Mn doped CsPbI₃ decreases obviously, while the lattice constant of Sn doped system decreases slightly, which improves the stability of the material. The deep level defects of both systems are close to conduction band and mainly capture electrons from conduction band. The doping of Mn and Sn elements improves the phonon energy distribution of the perfect system and enhances the heat transport capacity of the material. The nonradiative recombination coefficient of the holes in Sn doping system is much higher than that in Mn doping system and the nonradiative recombination coefficient of the two doping systems is higher than that of CsPbI₃ containing intrinsic defects I_i and I_Cs, so the impurity may introduce the nonradiative recombination center. These results provide data support for the experiment of Mn and Sn doped CsPbI₃ system, and provide a theoretical basis for the CsPbI₃ doping perovskite in experiments.