The invention discloses a lead-based functional nucleic acid colorimetric sensor and an application thereof. The colorimetric sensor comprises a molecule recognition element, a signal amplification element and a signal conversion element, wherein the molecule recognition element comprises lead ion deoxyribozyme consisting of a substrate chain and an enzyme chain; the signal amplification element comprises an isothermal amplification system comprising an amplification template; the signal conversion element comprises thioflavine. The colorimetric sensor is based on the lead ion deoxyribozyme, an isothermal index amplification reaction and a G-four chain liquid phase sensing technology, the molecular recognition element recognizes lead ions and produces an amplification product, the amplification product forms a G-quadruplex structure under the action of thioflavine, the lead ion concentration is calculated through fluorescence intensity detection, and the sensor is convenient, quick, high in sensitivity, high in specificity, resistant to high salinity and low in cost.