Lead halide perovskite quantum dots (PeQDs) are triggering a revolution in display technologies because of their near-unity photoluminescence quantum yield (PLQY), narrow band emission, wide tunable bandgap and facile synthesis. Therefore, they have been extensively investigated as color converters or emissive layers for light-emitting diode (LED) displays. However, the poor stabilities in the phase and structure of PeQDs make them hard to be practically applie, and the ultimate goal is therefore to improve the long-term stability of PeQDs. The poor stability of PeQDs originates from their inherent ionic nature. Under external conditions (such as light, heat, water and oxygen), PeQDs will decompose through interfacial reactions, leading to obvious fluorescence quenching. Although many efforts have been made to prepare robust PeQDs that are, to some extent, resistant to water, air, light, or heat exposure, he overall reliability of PeQDs shows limited improvement under the synergistic effects of multiple factors, which are usually the case in practical LED applications. We report ultrastable CsPbBr₃:Sr/PbBr(OH)/molecular sieve composites (Fig. 1) with a high photoluminescence quantum yield of 75% and high overall stability when exposed to water, blue light and heat, owing to (i) the increased formation energy of CsPbBr₃ PeQDs by Sr doping and (ii) good encapsulation by PbBr(OH) and molecular sieves. These composites maintain 54% of their initial intensity after being aged at 85°C and 150 mW/cm² for 720 min, which is superior to commercial green CdSe-based QDs. These promising composites are then used to produce Mini-LED backlights with a high luminous efficacy of 86 lm/W and a color area of ~124% of the National Television Standards Committee or 93% of the Rec. 2020 standards by combining them with red CdSe/CdS/ZnS QDs and a blue Mini-LED chip. We believe that highly reliable PeQDs can be achieved by building well-designed composite structures, thus enabling them to be practically applied in emerging lighting and displays.