Lead halide perovskite quantum dots (PQDs) are reported as a promising branch of perovskites, which have recently emerged as a field in luminescent materials research. However, before the practical applications of PQDs can be realized, the problem of poor stability has not yet been solved. Herein, we propose a trioctylphosphine (TOP)-assisted pre-protection low-temperature solvothermal synthesis of highly stable CsPbBr3/TiO2 nanocomposites. Due to the protection of branched ligands and the lower temperature of shell formation, these TOP-modified CsPbBr3 PQDs are successfully incorporated into a TiO2 monolith without a loss of fluorescence intensity. Because the excellent nature of both parent materials is preserved in CsPbBr3/TiO2 nanocomposites, it is found that the as-prepared CsPbBr3/TiO2 nanocomposites not only display excellent photocatalytic activity but also yield improved PL stability, enabling us to build highly stable white light-emitting diodes and to photodegrade rhodamine B.