Abstract: The first principle method was used to study the interaction mechanism between Bi⁰ and intrinsic defects(ODC(Ⅰ) and POL)in silica optical fiber, and the reaction path, formation energy, electronic structure and optical absorption spectrum were calculated. By analyzing the reaction paths, it was found that Bi⁰ is more likely to interact with the defect POL, forming the more stable reaction product, and Bi is bivalent at the center after the reaction. For the reaction of Bi⁰ with the intrinsic defect ODC(Ⅰ), the Bi atom forms a complex with the two Si atoms in the defect and produces an absorption peak in the near-infrared band of 1400~1500 nm. Our calculation results have important theoretical significance for the in-depth analysis of the interaction mechanism between Bi⁰ and intrinsic defects in silica optical fiber and the fabrication of bismuth-doped fiber.