The exploration of a dual-functional sensor is the key to effectively detect the Cr(VI) and Fe(III) cations in water, which is important to human health and environmental sustainability. Because of the phase stability and excellent luminescence, the rare-earth coordination polymers have great potential as dual-functional sensors. Here, we develop a Y_0.91Eu_0.09(H₂O)₂{C₆H₃(CO₂)₃}(MIL-92(Y):9%Eu³⁺)-based dual-function luminescent sensor on Cr(VI) and Fe(III), which exhibits excellent phase stability and dispersibility in water. The luminescence of MIL-92(Y):9%Eu³⁺ aqueous suspension quenches on Fe³⁺ with Stern-Volmer constant K_sv of 1.79 × 10³ M^-1 and limit of detection of 17 μM. The MIL-92(Y):9%Eu³⁺ aqueous suspension also has turn-off sensing ability towards Cr₂O₇^2- and CrO₄^2- with K_sv values of 3.5 × 10³ and 6.14 × 10³ M^-1, respectively. It has detection limitations of 10 and 5 μM on Cr₂O₇^2- and Cr₂O₇^2- ions, respectively.