The invention belongs to the technical field of detection of samples in environments and discloses application of a CdT3 QD@ZIF-8 nano composite material in chromium ion detection. The CdT3 QD@ZIF-8 nano composite material is dispersed into an HEPEs buffer solution, Cr<6+> and Cr<3+> ion standard solutions of different concentrations are added, a fluorescence spectrophotometer is used to detect fluorescence intensity, and a standard curve showing the change of F/F0 changing along with the concentration change of chromium ions is drawn; the CdT3 QD@ZIF-8 nano composite material is dispersed into an HEPEs buffer solution, different to-be-detected samples containing the chromium ions are added, the fluorescence spectrophotometer is used to detect the fluorescence intensity after chemical stability is achieved, the Cr<6+> content in the to-be-detected samples is determined through the standard curve, and Cr<6+> and Cr<3+> are distinguished through the fluorescence intensity. Directly compared with other chromium ion detection methods, the method is simple, low in cost, high in ion interference resistance and capable of distinguishing the Cr<3+> and the Cr<6+> and has huge advantages inthe chromium ion detection.