Semiconductor radiation detection materials， as core components of X-ray imaging technology， have been widely applied in medical imaging and industrial inspection. In recent years， three-dimensional （3D） perovskite materials have been demonstrated significant potential in semiconductor radiation detection due to their high atomic number， strong photoelectric conversion efficiency， and low fabrication cost. However， challenges for the materials， such as severe ionic migration-induced high dark current and instability， critically hinder their practical device applications. In this study， based on structural dimensionality modulation strategy， cyclohexylamine （CHA） was introduced to slice the 3D halogen-lead skeleton and to form layered perovskites CHA₂PbBr₄， achieving highly efficient and stable X-ray detection. Millimeter-sized CHA₂PbBr₄ single crystals were synthesized via a optimize-cooling solvothermal method， exhibiting with layered morphology with orientated growth. Benefiting from the suppressed ionic migration and dark current enabled by the layered structure， the CHA₂PbBr₄ single crystal exhibits a high resistivity of 1.64×10¹⁰ Ω·cm， as well as single-crystal device demonstrates a remarkable sensitivity of 3 791.4 μC·Gy_air^-1·cm^-2 under high electric field and an ultra-low detection limit of 84.55 nGy_air·s^-1. These results demonstrate that layered structural modulation of organic long-chains enables synergistic optimization of multi radiation detection performances， providing a potential candidate for high-performance X-ray detectors.