A study on Pb isotopes was conducted within the soil–plant–aerosol system. The results indicate that Pb isotopes serve as a suitable tool not only for tracing atmospheric pollution sources but also for tracking the Pb transfer process into and within plants. The main findings are as follows: 1) Pb isotopes in plants are a powerful tool for tracing Pb sources. When plants are removed from their original location, Pb isotopes in the whole plant or roots are suitable for tracing their growth sites; Pb isotopes in leaves are suitable for tracing aerosol particles in the surrounding environment; however, Pb isotopes in stems are not suitable for tracing Pb sources. 2) Pb isotopic fractionation occurs during the growth process of E. splendens Nakai (δ208Pb?????–???? = -4.31 to 0.30‰), and the extent of fractionation is larger than that of most mineral nutrients. This study also demonstrates that Pb isotopes in plants are a powerful tool for tracing the absorption and transport processes of Pb into and within the plant. Regardless of whether Pb is absorbed through the roots or leaves, lighter isotopes tend to be preferentially enriched in the subsequent tissues (from soil to root, from root to stem, and from leaf to stem within the plant), indicating non-selective absorption of Pb through ion channels. This is consistent with the diffusion effect on isotope ratio variation. Pb absorbed through the roots constitutes the main source of Pb in the plant. 3) The correlation between Pb isotope ratios could verify Pb pathways. Whether the correlation conforms to the principle of mass fractionation depends on whether Pb comes from one path or multiple pathways. This provides a new insight into understanding Pb sources in any physicochemical process or geological sample. 4) The addition of ethylene diamine disuccinic acid (EDDS, C??H??N?O?) promotes the uptake of Pb in the plant. However, it only affects the Pb concentration in the root and stem, but not in the leaf. This shows that altering soil state and promoting plant absorption are not ideal for reducing Pb pollution in soil for non-accumulator plants. The addition of EDDS in the soil also affects the variation in Pb isotope ratios within the plant. Compared with CK plants, heavier Pb isotopes were enriched in the EDDS-treated plants, which suggests a plant protection mechanism whereby heavier Pb isotopes are stored in biological macromolecules such as Pb-proteins/ligands to mitigate toxicity.