Perovskite CsPbBr₃ nanocrystals show excellent optical properties. However, the nanocrystals encounter a major challenge of poor stability. In this study, an effective approach is proposed for enhancing the stability of CsPbBr₃ nanocrystals via a dual passivation strategy, where the dual passivation layer is composed of alumina (Al₂O₃) and polymer ethylene-vinyl acetate (EVA). The Al₂O₃ coating on the CsPbBr₃ surface is realized by in situ oxidation of trimethyl aluminum (TMA), which passivated the surface defects while blocking the intrusion of water and oxygen. The EVA film is formed by a solution method, which can further block the water and oxygen, and form the flexible composite with perovskite CsPbBr₃ nanocrystals with enhanced stability toward water and heat. After soaking for 360 h and heating for 5 h, the photoluminescence (PL) intensity is higher than that without passivation. The polymer EVA packaging strategy provided CsPbBr₃ with excellent extensibility and flexibility at 100% and 200% tensile rates, the PL intensity remains 91% and 88% of the initial intensity, which returns to the initial value after stretching. The unique dual-protection structure significantly improves the water and thermal stability of the nanocrystals. The strategy might point out the direction for the future application of perovskites.