Mercury is one of the toxic and harmful heavy metal pollutants in the environment．It can enter the human body through the accumulation of food chain，thus damaging the human health．Recently，the control of mercury pollution has attracted much attention．The main detection methods for mercury in water involve inductively coupled plasma optical emission spectrometry（ICP－OES），atomic absorption spectrometry（AAS），atomic fluorescence spectrometry（AFS） and inductively coupled plasma mass spectrometry（ICP－MS）．However，these methods generally could not meet the requirements for convenient，rapid and sensitive on-site detection．Fluorescence detection method has the advantages of simple operation，rapid response，high sensitivity，good selectivity，and independent of large-scale instruments，which could fully meet the requirements for rapid detection of mercury in water．Based on the fluorescence quenching mechanism of Hg,2+, on carbon quantum dots（CQDs），a rapid method based on nitrogen and sulfur doped fluorescent CQDs was established for the detection of Hg,2+, in water．The fluorescent CQDs were synthesized by one-step hydrothermal method with sodium citrate，waste water and tetramethylthiuram disulfide as carbon，nitrogen and sulfur sources．Effects of the spectral properties as well as pH value，reaction time and component content on fluorescence intensity were all investigated．In the process of Hg,2+, detection，the relationships of fluorescence quenching with reaction time and pH value were further investigated，and the kinetic mechanism of quenching reaction was analyzed．The experimental results showed that the fluorescence quenching reaction of Hg,2+, on CQDs was rapid， which has a high quenching effect at pH 7.0，while the fluorescent CQDs had good selectivity and anti-interference ability for Hg,2+,．Under the optimized conditions，the detection limit for Hg,2+, was 0.95 μg/L，and the linear range was 1－6 μg/L.The accuracy of this method was investigated with surface water，and the recoveries for actual water samples ranged from 100% to 126%，with relative standard deviations（RSD） of 0.31%－3.9%.This method was suitable for rapid and convenient on-site detection of Hg,2+, in waste water samples.