In this manuscript, we report a facile synthesis of water-resistant CsPbBr₃ perovskite quantum dots (PQDs) loaded poly(methyl methacrylate) (PMMA) composite microspheres (CsPbBr₃@PMMA). The method is based on the precipitation polymerization of methyl methacrylate (MMA) in the presence of CsPbBr₃ PQDs. The CsPbBr₃@PMMA microspheres show a tunable size and a narrow size distribution, with the CsPbBr₃ PQDs being uniformly dispersed in the PMMA microspheres. The effective incorporation of PQDs is attributed to the strong coordination interactions between Pb ions on the surface of PQDs and carbonyl groups (C=O) from PMMA. Protected by the PMMA microspheres, the imbedded CsPbBr₃ PQDs show improved water resistance and storage stability. Further, a wide-color-gamut (129%) white light-emitting diode (LED) was demonstrated by combining the green-emitting CsPbBr₃@PMMA composite microspheres and red-emitting K₂SiF₆: Mn⁴⁺ with a blue LED, which enables to be used as backlights for liquid crystal displays.