<p><i>Bistorta vivipara</i> L. achenes (<i>B. vivipara</i> achenes), rich in phenolic acids and flavonoids, are a valuable food and medicinal resource. However, a detailed analysis of its individual components and their mechanisms remains unexplored. This study introduces solid-phase extraction (SPE) for selectively isolating and purifying total phenolic acids and flavonoids from <i>B. vivipara</i> achenes. The antioxidant potential of the extracts was evaluated using ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)), DPPH (2,2-diphenyl-1-picrylhydrazyl), and FRAP (ferric ion reducing antioxidant potential) assays. Results showed significant antioxidant activity in the total phenolic acid extract (125.1 ± 0.7&#xa0;mg GAE/g dry weight [DW]) and total flavonoid extract (1491.1 ± 19.9&#xa0;mg RE/g DW). Using online FRAP–high-performance liquid chromatography (FRAP–HPLC), seven antioxidant components were identified in the phenolic acid fraction and thirteen in the flavonoid fraction. Notably, protocatechuic acid, cryptochlorogenic acid, isochlorogenic acid A, isochlorogenic acid B, isochlorogenic acid C, shaftoside, isoshaftoside, isoorientin, taxifolin, and vitexin are reported for the first time as antioxidant constituents in <i>B. vivipara</i> achenes. These findings highlight <i>B. vivipara</i> achenes as a promising source of natural antioxidants and functional food ingredients. The SPE–FRAP–HPLC method enables comprehensive analysis by selectively enriching active compounds and enhancing sensitivity and accuracy compared with crude extracts. Furthermore, the application of online FRAP–HPLC facilitates real-time monitoring of the antioxidant activity of individual compounds during chromatographic separation, providing a detailed antioxidant activity profile of phenolic compounds in <i>B. vivipara</i> achenes.</p> Graphical Abstract <p></p>