Organic-inorganic metal halide glasses (OIMHGs) are promising materials for high-resolution X-ray imaging due to their transparency and tunable properties. However, their practical applications are severely limited by a transition from the glassy state to a polycrystalline phase under ambient conditions, leading to significant optical and performance degradation. Herein, the underlying mechanism of the rapid glass-to-crystal transition in methyltriphenylphosphonium-based hybrid materials (MTP)2MnBr4 is systematically investigated through X-ray absorption fine structure (XAFS) measurements, X-ray scattering analysis, and ab initio molecular dynamics simulations. For the first time, it is demonstrated that this transition is driven by the water molecules, which significantly influence the spatial arrangement of the organic (MTP+) and inorganic ([MnBr4]2−) components within the materials framework. To address the severe instability of this X-ray imaging glass in air, a novel composite encapsulation strategy is developed that integrates quartz glass layers with a waterproof parylene polymer coating. Consequently, the glass-to-crystal transition is substantially suppressed, enhancing the stability of the synthesized glass by over 100 times. This improvement enabled the material to maintain a spatial resolution of 26.3 lp mm−1 for more than twelve months. These findings underscore the critical role of environmental stability strategies in enhancing OIMHG-based scintillators for next-generation X-ray imaging applications.