This study investigates the defect tolerance of lead halide perovskite CsPbBr3 using first-principles calculations. The research reveals that CsPbBr3 exhibits high defect tolerance due to its electronic structure, where most intrinsic defects induce shallow transition levels, and only a few defects with high formation energies create deep transition levels. This allows CsPbBr3 to maintain good electronic quality despite the presence of defects. The study also shows that under Br-rich growth conditions, the formation energy of dominant defects is much lower, leading to higher defect concentrations. However, moderate or Br-poor growth conditions help reduce defect concentration. The defect tolerance of CsPbBr3 is attributed to the lack of bonding-antibonding interaction between the conduction and valence bands. The formation energy of defects was calculated using the HSE+SOC method, and the results indicate that Br-rich conditions can lead to high defect concentrations, while moderate or Br-poor conditions are preferable for minimizing defects. The study also highlights that the band structure of CsPbBr3 is different from covalent-bond semiconductors, which contributes to its defect tolerance. The findings provide insights into the high optoelectronic quality of CsPbBr3 despite the presence of point defects and guide experimental synthesis to reduce defect formation. The research is supported by the U.S. Department of Energy and uses computational resources from the National Energy Research Scientific Computing Center.This study investigates the defect tolerance of lead halide perovskite CsPbBr3 using first-principles calculations. The research reveals that CsPbBr3 exhibits high defect tolerance due to its electronic structure, where most intrinsic defects induce shallow transition levels, and only a few defects with high formation energies create deep transition levels. This allows CsPbBr3 to maintain good electronic quality despite the presence of defects. The study also shows that under Br-rich growth conditions, the formation energy of dominant defects is much lower, leading to higher defect concentrations. However, moderate or Br-poor growth conditions help reduce defect concentration. The defect tolerance of CsPbBr3 is attributed to the lack of bonding-antibonding interaction between the conduction and valence bands. The formation energy of defects was calculated using the HSE+SOC method, and the results indicate that Br-rich conditions can lead to high defect concentrations, while moderate or Br-poor conditions are preferable for minimizing defects. The study also highlights that the band structure of CsPbBr3 is different from covalent-bond semiconductors, which contributes to its defect tolerance. The findings provide insights into the high optoelectronic quality of CsPbBr3 despite the presence of point defects and guide experimental synthesis to reduce defect formation. The research is supported by the U.S. Department of Energy and uses computational resources from the National Energy Research Scientific Computing Center.