Abstract: The solvent extraction-based wet process is extensively utilized in spent fuel reprocessing, rendering the selection of extractants with outstanding extraction performance and robust chemical/radiation stability imperative. Tri-iso-pentyl phosphate (TiAP), a higher homologue of tri-butyl phosphate (TBP), boasts lower water solubility than TBP. It not only exhibits superior selectivity and extraction efficiency toward U(Ⅵ) and Th(Ⅳ) but also is less susceptible to third-phase formation during the extraction process. Consequently, TiAP is regarded as a highly promising alternative to TBP in the wet reprocessing of thorium-based nuclear fuel. In the spent fuel reprocessing process, extractants and their extraction systems are subjected to intense irradiation by various rays. This harsh irradiation environment inevitably induces changes in the molecular structure of extractants, such as chemical bond cleavage or recombination, thereby generating a series of radiolysis products. These radiolysis products tend to complex with metals, leading to difficulties in stripping and metal retention. As a major fission product in nuclear reactions, zirconium (Zr) can also be partially extracted by TBP, which impairs the decontamination efficiency of the extractant. Existing studies on irradiated TiAP primarily focus on evaluating its physicochemical properties or actinide extraction performance, leaving a research gap regarding metal ion retention—an aspect crucial for assessing extractant reusability. To address this gap, this study employed ⁶⁰Co as the γ-irradiation source. Combined with solvent extraction, inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the concentration of metal ions in the aqueous phase and calculate the extraction distribution ratio. The effects of extraction time, temperature, absorbed dose, dose rate, and aqueous acidity on Zr(Ⅳ) extraction and retention by irradiated TiAP were systematically investigated. Additionally, molecular dynamics (MD) simulation and density functional theory (DFT) calculation were integrated to explore the interaction modes between TiAP (along with its radiolysis products) and Zr(Ⅳ), as well as the underlying reaction mechanisms. The results demonstrat that within the absorbed dose range of 0-500 kGy, γ-irradiation with an absorbed dose of ≥200 kGy prolonged the time required for TiAP to reach Zr(Ⅳ) extraction equilibrium. Both the Zr extraction distribution ratio and its retention in the organic phase increase with the elevation of absorbed dose. The presence of nitric acid facilitates TiAP-mediated Zr(Ⅳ) extraction. For TiAP irradiated with an absorbed dose of ≥50 kGy, the Zr(Ⅳ) extraction distribution ratio increases with rising temperature and initial metal ion concentration. At an absorbed dose of 50 kGy, the dose rate exerts no significant impact on Zr(Ⅳ) extraction by TiAP. Furthermore, MD simulation and DFT calculation reveal that DiAP⁻, a radiolysis product of TiAP, is the primary contributor to Zr retention. These findings further enrich the understanding of TiAP’s radiolysis behavior and provide valuable data support for its potential application in spent fuel reprocessing.