<p>Ratiometric fluorescent probes have irreplaceable advantages of traditional single fluorescent probes, such as high accuracy, low background interference and high signal-to-noise ratio, which have attracted extensive attention but the preparation process is still a challengment. In this paper, fluorescent carbon dots (CDs) was prepared by hydrothermal treatment of citric acid and triethylamine, and electrostatic adsorption with Rhodamine, which was used to construct ratiometric fluorescent nanoprobes (WZ-L). Among them, rhodamine B was used as the reference signal of the fluorescent probe, which could eliminate part of the error. Carbon dots (CDs) were used as the identification signal for the detection of Hg²⁺. The probe specifically recognized Hg²⁺ in a wide pH range and had a well linear range (0-100 µL), which can be used for the quantitative detection of real Chinese herbal medicine samples. including Codonopsis and Codonopsis. In particular, the probe could provide a rapid response to Hg²⁺ within 2&#xa0;min with a detection limit as low as 7.94 µM. It is shown that this probe has a large application potential for future quantitative detection of Hg²⁺ in real samples, which provides a new analytical method and strategy for the subsequent detection of heavy metal ions.</p>