Despite recent advances in producing perovskite-nanocrystals-in-glass (PNG) for display application, it remains challenging to achieve ultrapure and large-area CsPbBr3 PNG-based flexible films with tunable green emission. Herein, we report a facile strategy to produce flexible film containing CsPbBr3 PNG. Specifically, the achievement of CsPbBr3 PNG with tunable green emissions (517-528 nm) is realized by elaborate regulation of the glass precursor concentration and thermal treatment temperature by an in situ growth method. With the integration of red-light-emitting CsPbBrxI3-x PNG powder, the color gamut of as-prepared white-light-emitting sources can cover up to 126.27% of the NTSC 1953 standard and 93.9% of the Rec. 2020 standard. Notably, flexible and large-area white-light-emitting films can be readily obtained by sandwiching and gluing mixed PNG powders between two layers of hydrophobic and transparent PET films. Intriguingly, as-prepared PNG films exhibit excellent hydrothermal, photostability, and long-term operation stability, making them promising for practical ultrahigh-definition displays.