Photo-thermal-refractive (PTR) glass was irradiated with γ-ray at the total dose of 0.35, 1, 10 and 100 kGy, respectively, and then annealed. Irradiation mechanism of the photo-thermal-refractive glass was studied by absorption spectroscope, luminescence spectroscope and electron paramagnetic resonance. The results showed that the absorption of the γ-irradiated PTR glass in the visible light was mainly caused by the Ag⁰, silver molecular clusters Ag₂, Ag₃, silver nanoparticles Ag_m⁰, and non-bridge oxygen hole center HC₁ and HC₂. Under different doses of γ-ray irradiation, valence state of the ions (Ag⁺, Ce³⁺) in the glass matrix changed. At the same time, non-bridged oxygen bonds in the glass matrix broke, generating non-bridged oxygen hole defects HC₁, HC₂ and Ag⁰. With the increase of the radiation dose, silver molecular clusters Ag₂ and Ag₃ generated, and the concentration of HC₂ center in the glass matrix increased, resulting in enhanced absorption near 639 nm. After being irradiated and annealed at 250 ℃, HC₁ and HC₂ defect centers was bleached. Silver molecules appeared after annealing at 430 ℃, of which absorption peak had a redshift and was broadened with the increase of annealing duration.