Ratiometric fluorescence sensing methods are widely used in analysis and detection due to their high sensitivity and stability. In this work, a ratiometric fluorescence method for sensitive detection of Hg2+ was established using a gold nanoclusters/carbon quantum dots (AuNCs/CQDs) nanohybrid probe. The AuNCs/CQDs nanohybrids probe were simply constructed by mixing blue-light-emitting gold nanoclusters (AuNCs) with an orange-emissive carbon quantum dots (CQDs). The probe had two fluorescence emission peaks at 434 nm and 561 nm when the excitation wavelength was 375 nm. With the addition of Hg2+, the fluorescence at 434 nm decreased and the fluorescence at 561 nm remained unchanged; the fluorescence intensity ratio Δ(F434/F561) and Hg2+ concentration have a good linear relationship in the range of 8.32 × 10-7 to 7.69 × 10-5 mol L-1, and the limit of detection (LOD) is 3.58 × 10-7 mol L-1. The method was applied in the detection of Hg2+ in cosmetics and wastewater, and has potential applications for detecting Hg2+ in other samples.