Abstract: In this work, the changes in surface morphologies, micro-structures, chemical bond vibrations, and optical properties of fused silica crystals after irradiated with 355 nm nanosecond laser at different energy densities were investigated by a field emission scanning electron microscope (FE-SEM) and infrared spectrum (IR) analysis techniques. The FE-SEM results indicate that the damage area after irradiation increases nonlinearly with increase of laser energy density. In the damaged region, the relative content of Si element significantly increases, while the relative content of O element decrease, and cracks appears around it. Meanwhile, it has been clearly observed that filamentous materials are generated in the melting zone, and their origins are discussed in detail. Infrared spectrum analysis shows that after irradiation with lower energy densities (4~8 J/cm²), the intensity of vibration modes from Si-O-Si bonds generally decreases and red-shift for their peak positions may occur, as well as the surface reflectivity reduces obviously. As the energy density increases (10~13 J/cm²), the intensity of Si-O-Si bond vibration modes recovers to some extent, and the surface reflectivity remarkably enhances. In addition, the reststrahlen band of SiO₂ located between the 433 and 557 cm⁻¹ vibration modes disappears after 4 J/cm² irradiation, and partially restores after 13 J/cm² irradiation. These research results provide reference experimental data and theoretical foundations for the full use of fused silica crystals in ICF engineerings.