A 60 kW electron beam is used to study the microstructure and optical property evolutions as well as laser induced damage threshold of fused silica after irradiation at room temperature. Optical microscopic results indicate that cracks appear at the surface of SiO2 after electron beam irradiation, owing to the thermal effect, and that the crack density and size increase with increasing radiation dose. The morphology of the surface cracks is analyzed by using atomic force microscope and the width of crack is about 1 μm. In addition, there are a large number of debris particles with sizes of 0.1-1 μm on the surface. From the optical absorption spectrum of each of all samples, a weak absorption peak at 394 nm is observed and the absorbance increases at the beginning then decreases with increasing electron-radiation dose. Before and after irradiation, three absorption bands at 460 nm, 496 nm and 520 nm are clearly observed and their intensities first increase and then decrease, which is consistent with the results of absorption spectra. The effect of electron dose on the laser induced damage threshold (LIDT) at 355 nm is investigated and the results indicate that the LIDT decreases with increasing dose. At the lower electron doses, the color centers are responsible for the decrease of LIDT. However, at the higher electron doses, the decrease of LIDT is due to the light modulation and absorption induced by microscale cracks and debris particles at the surface of irradiated fused silica.