In this work, a ratiometric fluorescence system was designed for the detection of trace UO22+ in water based on the inner filter effect (IFE) between gold nanoparticles (AuNPs) and gold nanoclusters (AuNCs). IFE-induced fluorescence quenching was achieved due to the enhanced complementary overlap between the absorption spectra of AuNPs and the emission spectrum of AuNCs after the addition of UO22+. Blue carbon dots (B-CDs) were added to serve as reference fluorophores to expand the color tonality and make human eye recognition easier. The ratiometric fluorescent sensor demonstrated a unique fluorescence color change from red to blue when different doses of UO22+ were added, with a detection limit of 8.4 nM. Furthermore, the ratiometric fluorescent sensor was effectively used for UO22+ determination in real-world water samples, with acceptable recoveries.