In this paper, a novel dendritic chemosensor was designed and synthesized. Specific dual-channel fluorescent sensing for Hg 2+ was investigated. The probe represented dual recognition sites and segmented detection behaviors, which can be deduced to the dethioacetalization reaction promoted by Hg 2+ and the coordination reaction between Hg 2+ ions and the nitrogen atoms in triazole rings of probe. The probe was proved to selectively recognize Hg 2+ ions in aqueous solution and it showed a high selectivity, a low detection limit (12 nM), a short response time, and a significant fluorescence enhancement (at 610 nm) with high fluorescence resonance energy transfer efficiency (99 %) between the energy donor and the energy acceptor. Moreover, the energy levels of the energy donor-acceptor pairs calculated by DFT theory were used to illustrate the different FRET efficiencies of probe and probe with Hg 2+ .