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SiO2 is the major mineral substance in the upper mantle of the earth. Therefore, studies of the silica-coated materials under high-pressure are essential to explore the physical and chemical properties of the upper mantle. The silica-confined CsPbBr3 nanocrystals (NCs) have recently attracted much attention because of the improved photoluminescence (PL) quantum yield, owing to the protection of silica shell. However, it remains considerable interest to further explore the relationship between optical properties and the structure of CsPbBr3@SiO2 NCs. We systemically studied the structural and optical properties of the CsPbBr3@SiO2NCs under high pressure by using diamond anvil cell (DAC). The discontinuous changes of PL and absorption spectra occurred at～1.40 GPa. Synchrotron X-ray diffraction (XRD) studies of CsPbBr3@SiO2 NCs under high pressure indicated an isostructural phase transformation at about 1.36 GPa, owing to the pressure-induced tilting of the Pb-Br octahedra. The isothermal bulk moduli for two phases are estimated about 60.0 GPa and 19.2 GPa by fitting the equation of state. Besides, the transition pressure point of CsPbBr3@SiO2 NCs is slightly higher than that of pristine CsPbBr3 NCs, which attributed to the buffer effect of coating silica shell. The results indicate that silica shell is able to enhance the stabilization without changing the relationship between optical properties and structure of CsPbBr3 NCs. Our results were fascinated to model the rock metasomatism in the upper mantle and provided a new'lithoprobe' for detecting the upper mantle.