This study introduces a novel method for deep-tissue hydrogel formation using X-ray-activated polymerization, overcoming the limitations of traditional UV/Vis light-based techniques. The method utilizes a low-dose X-ray-activated persistent luminescent phosphor, which triggers on-demand in situ photo-crosslinking reactions, enabling hydrogel formation in deep tissues, including thick bovine bone. The phosphor, synthesized as HNTs@YF₃:Tb³⁺, is embedded in halloysite nanotubes and exhibits strong visible luminescence and afterglow, serving as a light source for polymerization. The system was validated through in vitro and in vivo experiments, demonstrating high biocompatibility and the ability to form hydrogels in deep tissues. The study highlights the potential of X-ray-activated polymerization for precise and safe deep-tissue hydrogel formation, with applications in tissue repair, regenerative medicine, and bone tissue engineering. The method offers advantages such as spatial controllability, non-contact external stimuli, and minimal environmental requirements. The results suggest that X-ray-activated polymerization could revolutionize biomedical applications by enabling deep-tissue hydrogel formation with unprecedented depth and precision.This study introduces a novel method for deep-tissue hydrogel formation using X-ray-activated polymerization, overcoming the limitations of traditional UV/Vis light-based techniques. The method utilizes a low-dose X-ray-activated persistent luminescent phosphor, which triggers on-demand in situ photo-crosslinking reactions, enabling hydrogel formation in deep tissues, including thick bovine bone. The phosphor, synthesized as HNTs@YF₃:Tb³⁺, is embedded in halloysite nanotubes and exhibits strong visible luminescence and afterglow, serving as a light source for polymerization. The system was validated through in vitro and in vivo experiments, demonstrating high biocompatibility and the ability to form hydrogels in deep tissues. The study highlights the potential of X-ray-activated polymerization for precise and safe deep-tissue hydrogel formation, with applications in tissue repair, regenerative medicine, and bone tissue engineering. The method offers advantages such as spatial controllability, non-contact external stimuli, and minimal environmental requirements. The results suggest that X-ray-activated polymerization could revolutionize biomedical applications by enabling deep-tissue hydrogel formation with unprecedented depth and precision.