In this paper, a tapered optical fiber sensor based on chelating agent functionalization is presented for the quantitative detection of low concentration heavy metal Pb²⁺. The sensor is made of single mode and four core fiber, and the middle four core fiber is tapered to a diameter of 15 microns. On this basis, ethylenediamine tetraacetic acid was used as a metal chelating agent to coat on the surface of a tapered four-core optical fiber sensor, so as to achieve high sensitivity detection of lead ions Pb²⁺. Experimental results show that the detection limit of Pb²⁺ is 1 ng/mL. In addition, the sensor has the advantages of good stability, simple preparation process and fast response speed.