The increasing deterioration of ecosystem derived from heavy metals residues brings about the environmental and food contamination, which presses the exploration of facile platform for monitoring heavy metals. Herein, a ratiometric fluorescence sensor was designed for Hg detection based on the compound of UiO-66-NH and Ru(bpy) (Ru@UiO-66-NH) which was synthesized by situ encapsulation. The innovative composite displayed two emission peaks at 437 and 604 nm, and the addition of Hg could only quench the blue fluorescence due to static quenching and photo-induced electron transfer mechanism, providing an internal standard to promote the precision. Under optimal conditions, the ratiometric Ru@UiO-66-NH probe revealed outstanding anti-interference capability and performed with a great limit of detection (LOD) of 0.053 μM for Hg, which was 2-fold lower than that of single-color UiO-66-NH. By merit of Ru@UiO-66-NH, test hydrogels were fabricated to provide a tactics for visual, rapid and on-site detection of Hg. Additionally, the dual-emitting sensing platform presented satisfactory recoveries and reliabilities in lake water, tap water, and drink water, demonstrating the application potential of this proposed ratiometric fluorescence sensor for monitoring Hg.