A sensitive fluorescence strategy was constructed for the detection of alpha-glucosidase activity based on AgInZnS QDs. The AIZS QDs which were synthesized by hydrothermal method have a fluorescence emission wavelength of 554 nm. Ce.sup.4+ was able to oxidize p-phenylenediamine (PPD) to generate oxPPD, which can quench the fluorescence of AIZS QDs through dynamic quenching. When alpha-glucosidase was introduced into the system, L-ascorbic acid-2-O-alpha-D-glucopyranosyl (AAG) could be hydrolyzed to form ascorbic acid (AA), which can reduce Ce.sup.4+ and prevent the oxidation of PPD. Thus, the dynamic quenching process was blocked accompanying with the fluorescence recovery of AIZS QDs. The developed detection system for alpha-glucosidase displayed a good linear relationship between 0.01 and 0.16 U·mL.sup.-1 with a detection limit of 0.0073 U·mL.sup.-1. The sensing platform with high feasibility and anti-interference is a competitive alternative applied to alpha-glucosidase-related diagnostics.