The all-inorganic CsPbX₃ (X=Cl, Br, I) perovskite nanocrystals have been widely applied in optoelectronic devices due to their excellent optoelectronic properties. However, their poor stability remains one of the main factors restricting their commercial development. This research focuses on improving the stability and solid-state luminescence performance of CsPbBr₃ nanocrystals. The porous MIL-53 (Al) metal-organic frameworks (MOFs) with outstanding hydrophobic properties was chosen as the encapsulation matrix. CsPbBr₃ nanocrystals were grown in situ within the MIL-53 (Al) channels by using a thermal injection process to successfully synthesize CsPbBr₃@MIL-53 nanocomposite phosphors with outstanding solid-state luminescence performance and high stability. MIL-53 chelates with CsPbBr₃ nanocrystals through benzene rings and organic ligands, firmly anchoring nanocrystals in the pores. This not only protects the CsPbBr₃ nanocrystals from external environmental influences but also effectively prevents aggregation between nanocrystals, thereby avoiding quenching of solid-state fluorescence. Additionally, the COO^- functional groups in MIL-53 bind with the unpaired Pb²⁺ on the surface of CsPbBr₃ nanocrystals, passivating the surface defects and suppressing non-radiative carrier recombination. Furthermore, the contained benzene rings and organic long chains endow the nanocomposite phosphors with excellent hydrophobic properties. The synergistic effect of these factors significantly enhances the optical performance and water stability of CsPbBr₃@MIL-53 nanocomposite phosphors. As a result, photoluminescence quantum yield (PLQY) of CsPbBr₃@MIL-53 nanocomposite phosphors reaches 75.4%, which is 2.3 times of that of solid-state CsPbBr₃ nanocrystal powders (33.2%). Even after being completely immersed in water for 10 h, its fluorescence intensity can still maintain 75.6% of the initial value. Finally, the green-emitting CsPbBr₃@MIL-53 nanocomposite phosphors were applied to white LED devices, achieving a wide-color-gamut coverage area of 126% NTSC and 85% Rec. 2020, which demonstrates its application prospects in wide-color-gamut display devices.