To reveal the utilization value of leaf, stem, and root of Artemisia argyi, a rapid online liquid microextraction combined with a high‐performance liquid chromatography coupled with 2,2‐nitrogen‐di (3‐ethyl‐benzothiazole‐6‐sulfonic acid) diammonium salt antioxidant assay system was established for analysis of antioxidants in the leaf, stem, and root of A. argyi, and a calibration quantitative method of antioxidant activity with equivalent chlorogenic acid was proposed. Thirty‐three positive peaks were identified; among them, 12 compounds were found that possess good antioxidant activity including eleven organic acids (components 2–4, 8, 11–14, 17, 19, and 21) and one flavonoids (component 22). The proposed calibration quantitative method avoided the influence of content of compound and compared the extent of radical scavenging capacity of five antioxidant compounds, which were ranked as follow: 3,5‐dicaffeoylquinic acid > 3,4‐dicaffeoylquinic acid ≈ 4,5‐dicaffeoylquinic acid > 1,4‐dicaffeoylquinic acid > chlorogenic acid. In conclusion, this study provided composition and biological potential for the future development of the leaf, stem, and root of A. argyi. It is believed that the online liquid microextraction combined with high‐performance liquid chromatography based antioxidant assay system can be widely used for the rapid screening of natural antioxidant components in the different parts of natural products.