Radiation-induced defects in nanomaterials are an important aspect of the research on the effects of radiation on materials. Recently, the research on radiation-induced defects in semiconductor materials, low-dimensional materials, and high-specific-surface porous materials has become a new application of radiation technology. Radiation-induced nanomaterial defect engineering has the potential to be used to improve the electromagnetic, catalytic, adsorption, and mechanical properties of nanomaterials and will play an important role in materials science, electronic-device development, catalysis, and environmental science. Therefore, this review presents the recent progress and state-of-art in the formation and tuning mechanism of radiation-induced defects in nanomaterials and provides a direction for future development.