The invention discloses a ratio-type variant 
receptor mercury 
ion fluorescent probe and its preparation method and use. The ratio-type variant 
receptor mercury 
ion fluorescent probe has the advantages of simple synthesis processes, good light stability, the largest emission 
wavelength of 550nm and good 
chemical stability under neutral conditions. Through 
amide functional group tautomerism, the 
receptor has a deformation capability of combination of an 
imidic acid isomer and mercury ions and combination of an 
amide isomer structure and other 
metal ions so that the receptor has mercury 
ion specific combination selectivity. The probe with the mercury ion produces 
fluorescence spectrum 
red shift to 633nm and the 
fluorescence spectrum is enhanced by 9 times. After bonding to other 
metal ions especially such as congener 
zinc ion and 
cadmium ions, the probe has no obvious 
fluorescence change and has mercury ion 
specific fluorescence signal selectivity. The probe realizes mercury ion specific ratio identification, can be used in detection of mercury ions in cells and has a wide application prospect in detection of mercury ions in other organisms and environments.