This study examines the chemical composition and antioxidant properties of iron walnut oil (IWO) from different Chinese regions, using ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry for the analysis of phenolic compounds. Regional variations were identified in fatty acid profiles, with elevated α-linolenic acid levels observed in samples from cooler climates (e.g., Liaoning, sample 1) that were 60% higher than in samples from warmer regions (e.g., Sichuan, sample 2). Antioxidant properties, quantified using 1,1-diphenylpicryl phenyl hydrazine (DPPH), 2,2-azinobis-3-ethylbenzothiazoline-6-sulfonate (ABTS), and Ferric ion reducing antioxidant power (FRAP) assays, corresponded to both oil polyphenol content (up to 62.91 mg/kg) and γ-tocopherol concentrations (268.68-525.05 mg/kg). Nineteen phenolic acids and flavonoids were identified, including ellagic acid, gallic acid, p-hydroxybenzoic acid, syringic acid, vanillic acid, quercetin, caffeic acid, ferulic acid, p-coumaric acid, coniferol, and pinoresinol. This comprehensive analysis underscores the nutritional and therapeutic potential of IWO, and delineates the impact of geographic and environmental factors on its quality, providing a scientific foundation for further research and development aimed at enhancing food industry standards and exploring natural product chemistry.