Abstract: Based on specific colorimetric recognition of Hg²⁺ with PNTU probe, a method for the determination of Hg²⁺ by fluorescence quenching was established. In the ethanol solution of 4-bromo-1,8-naphthalene anhydride, 2 mL of 80% (mass fraction) hydrazine hydrate solution was added dropwise. After filtering, washing with ethanol and water and drying, pyrrolithane of 10 mL was added. Then reaction was running under the protection of nitrogen to give reddish-brown solid. The reddish-brown solid was dissolved in 15 mL of acetonitrile, and 1 mL of phenyl isothiocyanate was added by stirring at room temperature. After the reaction was completed, the PNTU probe was obtained after vacuum concentration and washing with water. PNTU probe solution was evenly mixed with a mixture of acetonitrile-4-hydroxyethyl piperazine ethanesulfonic acid buffer solution at volume ratio of 8∶2, then Hg²⁺ sample soution was added, and fluorescence intensity of the system was measured by fluorescence quenching. The results showed that the fluorescence intensity of PNTU system decreased obviously when Hg²⁺ was added, following color of the solution changed from yellow to orange-red, and the PNTU probe could detect Hg²⁺ in the presence of other metal ions. Linear relationship between concentration of Hg²⁺ and magnitude of decrease in fluorescence intensity of the system was kept within 20.0 μmol·L^-1, with detection limit (3S/N) of 1.8 nmol·L^-1. Recovery test was made by standard addition method on actual water samples at 3 concentration levels, giving results in the range of 99.6%-104%, and RSDs (n=5) of the determined values ranged from 0.85% to 2.6%. Detection strips based on PNTU probe were prepared, which could easily and quickly detect whether Hg²⁺ exists in the sample.