Carbon dots (CDs) with blue emission were synthesized by solvothermal method using hydroquinone and 5-aminoisphthalic acid as precursors. The strong oxidation of ClO caused the fluorescence quenching of CDs at 405 nm, and synchronously generated a new emission peak at 500 nm. Furthermore, upon the addition of Cu to CDs-ClO system, the green fluorescence at 500 nm was quenched, while the blue emission at 405 nm remained unchanged, due to the complexation between Cu and the amino group on the CDs surface. Meanwhile, the fluorescence color of system changed from blue to bright green and then to dark blue by sequentially increasing the concentrations of ClO and Cu. The fluorescence signal of F/F exhibited a linear relationship with the concentration of ClO and Cu in a certain range, respectively. Thus, a ratiometric fluorescence sensor based on the obtained CDs were developed to sequentially detect ClO and Cu with detection limits of 0.40 μM and 0.31 μM, respectively. Additionally, the CDs were mixed with polyvinyl alcohol hydrogel to form test strips, which were successfully used for visual detection of ClO and Cu. Satisfactory results were also obtained in the analysis of ClO and Cu in actual water samples.