Metal halide perovskite nanocrystals (PNCs) have demonstrated intense luminescence and short emission lifetime, which perfectly match the requirements of X-ray fast scintillators. However, the poor stability of PNCs restricts their applications. Herein, CsPbBr3 NCs in a wide band-gap Cs4PbBr6 perovskite single crystal (PSC) matrix for efficient light extraction is reported. Benefitting from the protection of the PSC matrix and the perfect lattice matching, the PNCs embedded PSC show highly minimized nonradiative recombination and greatly improved stability. Moreover, by controlling the chemical equilibrium, the self-absorption of PNCs is reduced and the quantum yield increased to 78.5%. Furthermore, the PNCs embedded PSC demonstrates an appreciable light yield of 15,290 photons MeV−1, much higher than the commercial scintillator BGO (8200 photons MeV−1), and a decay time of 12.8 ns, significantly shorter than almost all the representative scintillators. This work demonstrates unambiguously the potential of PNCs embedded PSC for next-generation fast scintillators.