<p>Celery is highly susceptible to postharvest spoilage, significantly diminishing its nutritional and commercial value. This study applied various postharvest treatments to celery, including high voltage electric field (HVEF), 4% carbon dioxide (CO₂), 8% CO₂, 4% CO₂ + HVEF, and 8% CO₂ + HVEF, to assess their impact on the organoleptic properties of celery and the alteration of chemical constituents during storage. The results revealed that these treatments effectively delayed the yellowing and rotting of celery post-harvest, maintaining the stability of the cell structure, inhibiting the degradation of chlorophyll, and regulating the synthesis and metabolism of secondary metabolites. These metabolites include total phenols, total flavonoids, apigenin, vitamin C (Vc), and volatile organic compounds (VOCs), as well as the scavenging activity of 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals. Among the various treatments, the 8% CO₂ + HVEF treatment exhibited superior efficacy, which increasing the contents of apigenin, total ketones, total phenols, and Vc by 220%, 310%, 220%, and 280%, respectively, and enhancing DPPH radical scavenging activity by 2.1-times compared to the control. HS-SPME-GC/MS analysis indicated that the 8% CO₂ + HVEF effectively preserved VOCs, particularly D-limonene, and significantly increased the expression of genes such as <i>AgPAL1</i>, <i>AgDFR2</i>, and <i>AgTPS25</i>, which are involved in the synthesis of total phenols/flavonoids and terpenes. At the end of storage period, the composite score method was employed to evaluate the treatment combinations, with the 8% CO₂ + HVEF treatment achieving a significantly higher score than other groups. In conclusion, the co-treatment of HVEF and CO₂ effectively modulates the synthesis and metabolism of secondary metabolites in celery post-harvest, thereby extending its storage period and providing a theoretical foundation for its application in postharvest storage and preservation of horticultural products.</p>