The aldehyde compounds such as p-hydroxybenzaldehyde, pyrrole formaldehyde and acetaldehyd were introduced into the fluorescein thiohydrazide via the Schiff base reaction, the resulting compounds of TFP3, TFP4 and TFP5 could detect mercury with high selectivity and sensitivity. In further study, it was found that when the 7.5 mu mol/L Hg(2+ )was added, the fluorescence enhancement of TFP3, TFP4 and TFP5 at 530 nm of fluorescence spectrum appeared more than 30 times and the detection limits were 7.22x10(-8), 1.03x10(7) and 1. 28x10(-8) mol/L, respectively. In addition, the cellular imaging experiment exhibited that the probe had good biocompatibility and low toxicity, and may have practical application in the biological system.