Silica glass is widely used in optical systems due to its stable performance, broad transparent wavelength range and low absorption loss. While research and application of silica glass has advanced to the vacuum ultraviolet band, there remains a gap in understanding its absorption loss characteristics and the impact of irradiation in this range. By investigating the energy band structure, Urbach tail energy, and other characteristics of the short-wave absorption edge of silica glass, the microscopic defects of silica glass can be obtained and linked to its properties. This is of great significance for the in-depth understanding of the mechanisms related to various properties of silica glass from the microscopic point of view and its performance degradation under irradiation. In this paper, gamma rays and vacuum ultraviolet radiation were used for irradiation tests on silica glass. The optical bandgap, Urbach tail energy and oxygen vacancy defect (ODC) content of silica glass before and after irradiation were calculated by measuring the VUV absorption edge spectra, which were divided into three regions: strong absorption region, exponential absorption region and weak absorption region. Variations in atomic structure and defects in silica glass under different irradiation sources and doses were then discussed.