In this study, polyvinyl alcohol (PVA)-modified polyethylene glycol terephthalate (PET) films were prepared using γ-radiation crosslinking. The PVA molecules formed a crosslinking network after γ-irradiation and were loaded onto the surfaces of the PET films. The samples were analyzed by Fourier-transform infrared spectroscopy and scanning electron microscopy to demonstrate that the PVA was successfully anchored to the PET film surfaces. Light transmission tests revealed that the modified films maintained good optical properties with a light transmission of 89%. Whether under high-temperature, high-humidity, or low-temperature freezing conditions, the tests revealed that the samples exhibited good anti-fogging performance. Saturated water absorption tests revealed that the anti-fogging properties of the modified PET films were derived from the water absorption of the PVA crosslinking network, where the PET film under 12.43% loading showed a saturated water absorption of 50%.