<p>This study focuses on the environmental characteristics of mercury (Hg) and develops a system using nitrogen-doped blue fluorescent carbon quantum dots (N-CQDs) to analyze the presence of Hg in water and soil samples. Analysis of ultraviolet absorption spectrum, fluorescence spectrum, and infrared spectrum demonstrates excellent photoluminescence and stability, with the surface exhibiting diverse functional groups. The optimum conditions for N-CQDs to detect Hg²⁺ are pH 7, a reaction temperature of 25°C, and a reaction time of 5 min. Ion selectivity and anti-interference experiments demonstrate the system's strong sensitivity and selectivity. The calculation equation was derived from the linear relationship between the N-CQDs analysis system and the concentration of Hg²⁺. It is appropriate for analyzing low concentrations of Hg²⁺ in the environment, with a correlation coefficient of 0.994 and a detection limit (LOD) value of 3.271 μM at Hg concentrations ranging from 0 to 4 μM. Furthermore, it has the capability to identify the presence of toxic Hg²⁺ in tap water, river and lake water, as well as soil samples, with a recovery rate ranging from 96.7% to 105.2%. An extensive examination of the Stem-Volmer equation, UV–visible absorption spectra, and Fourier transform infrared spectrum at different temperatures reveals that the process responsible for the decrease in fluorescence is static quenching.</p>