A CdS nanocrystalline fluorescent probe (SiO2/CdS NCs) fixed on a silicon-based surface is prepared by selectively depositing CdS nanocrystallines on the surface of carboxylated SiO2 through a surfaceion-induced homogeneous precipitation technology, a result shows that the CdS nanocrystallines are dispersed and fixed on the SiO2 surface, the SiO2 dielectric effectively prevents aggregation of theCdS nanocrystallines, and the prepared SiO2/CdS NCs fluorescent probe has relatively strong fluorescence emission and relatively good light stability. In addition, compared with other metal ions, theCu<2+> is easier to replace Cd<2+> ions of a CdS lattice to form a CuS/CdS heterojunction, and has relatively strong fluorescence quenching efficiency, and on the basis, a selective fluorescent probebased on SiO2/CdS NCs is developed to realize high-sensitivity detection of trace Cu<2+> in tea leaves. Compared with a stable CdS nanocrystalline fluorescent probe based on an organic solvent, the SiO2/CdS NCs fluorescent probe is insensitive to the pH of the solution, an analysis procedure is simple, the selectivity is relatively high and the linear range is wide. Compared with a nanocrystalline fluorescent probe based on a coated SiO2 protective shell, the SiO2/CdS NCs fluorescent probe is simple in preparation process and good in analysis reproducibility.