In this paper, regulation of self-assembly properties of thiacyanine dye (Dye2) by nucleic acid aptamer (T30695) was used to construct a specific recognition unit for detecting Pb²⁺. G-quadruplexes were formed to interact with dye 2 monomers, which could disassemble dimers of Dye2 into monomer, in the presence of Pb²⁺. The absorption vales at 422 nm via 445 nm was used as a specific recognition signal to achieve the purpose of specificity and high sensitivity identification of Pb²⁺ only by UV-vis spectra. This system has a good linear relationship from 0.25 to 10.00 μmol/L (R² = 0.992 7), and the detection limit is 0.115 μmol/L.