Detection and discrimination of allura red (AR) are highly desired for food safety, which is still challenging due to the abundant of food pigments and their minor differences in optical properties. Heren, we developed a fluorescence assay for quantitative detection and discrimination of AR utilizing the dual function of sulfur nanodots (S-dots), where S-dots acted as both the fluorescence indicator and the decomposition reagents for AR. The fluorescence of S-dots was quenched by AR and gradually recovered, attributed to the decomposition effects of S-dots and etched reagents. AR was detected as low as 5 nM, and discrimination of AR was realized through observing the fluorescence recovery. The detection and discrimination of AR in practical food samples were also realized, and a portable test kit was fabricated for the on-site detection of AR. The presented work provided a new clue for designing sensors, exhibiting application potential for guarantee food safety.