Abstract: CXCR4 is a chemokine receptor widely overexpressed on the surface of various tumor cells. Given its pivotal role in tumor invasion, metastasis, and recurrence, it has emerged as a key target in molecular imaging. Radiochemical purity is one of the critical quality attributes (CQAs) of diagnostic agents. For the novel ⁶⁸Ga-labeled CXCR4-targeted diagnostic agent with a cyclic octapeptide scaffold designed in this study, an analytical method based on high-performance liquid chromatography coupled with a radioactive detector (Radio-HPLC) was established for the determination of its radiochemical purity. Validation experiments focusing on specificity, linearity, repeatability, and quantification limit (QL) confirmed that the method could accurately detect the main radioactive component and impurities of the agent. The validation results showed that the resolution between the main component and impurities all exceeded 1.5, demonstrating the method’s capability to identify potential radiochemical impurities; the correlation coefficient was greater than 0.99 over the injected radioactivity range of 0.011 to 1.11 MBq; the relative standard deviation (RSD) of the radiochemical purity repeatability test was 0.4%; and the QL was 0.011 MBq, enabling the quantitative determination of 1% radiochemical impurities. This analytical method is rapid, specific, and good consistency, and can serve as a reliable quality control tool for subsequent drug quality research and process development.