Abstract: With the growing demand for flexible, lightweight, and highly sensitive radiation detection technologies, particularly in medical imaging and wearable electronics, the development of new radiation-responsive materials has become an urgent challenge. In this study, we report the design and synthesis of a one-dimensional magnesium-based coordination polymer single crystal, denoted as ADC-Mg, via solvothermal reaction between 9, 10-anthracenedicarboxylic acid and MgCl₂ in a DMF/H₂O solvent system. Single-crystal X-ray diffraction reveals that ADC-Mg adopts a monoclinic structure with a well-defined MgO₆ octahedral coordination geometry and a stabilized three-dimensional supramolecular network. The material exhibits excellent thermal stability, a high resistivity of 1.03 × 10¹² Ω·cm, and a direct bandgap of 2.84 eV, confirming its semiconducting nature. Under X-ray irradiation, ADC-Mg displays a linear current–voltage (I–V) response, rapid switching behavior, and an enhanced signal-to-noise ratio (SNR). A powder-pressed device demonstrates a sensitivity of 17.273 μC  Gy^-1  cm^-2 and a low detection limit (LOD) of 1.27  μGy/s under a bias of 100 V. Furthermore, by blending ADC-Mg with epoxy resin, a flexible composite film was fabricated using a thermoplastic process, achieving a significantly enhanced sensitivity of 222.920 μC  Gy^-1  cm^-2. Carrier mobility–lifetime product (μτ), extracted by fitting the Hecht equation, reaches 1.02×10^-4 cm²  V^-1, surpassing that of commercial α-Se. These results indicate that ADC-Mg combines structural tunability, outstanding charge transport, and compatibility with flexible electronics, making it a promising candidate for next-generation high-performance X-ray detection platforms.