Effects of dynamic high pressure microfluidization (DHPM), microwave, ultrasound, maceration and high temperature, on the phenolic acids and antioxidant activity of Artemisia selengensis Turcz (AST) were investigated. Microwave exhibited the best extraction efficacy on phenolic compounds and flavonoids with the content of 40.30 μg GAE/mg Extract, and 37.75 μg RTE/mg Extract, respectively. Microwave extract (MWE) also showed the strongest DPPH· and HO· scavenging ability (IC50 value of 0.23 and 0.50 mg/mL, respectively), and reducing power (Ab0.3 value of 0.23 mg/mL). Quinic acid, 3 caffeoylquinic acids (CQAs), 2 coumaroylquinic acids, 4 dicaffeoylquinic acids (diCQAs) were identified as the major phenolic acids in AST using HPLC-QTOF-MS/MS, and 3-CQA (63.71 μg/mL) showed the highest content followed by 1,5-diCQA (17.91 μg/mL) and 3,5-diCQA (13.50 μg/mL). MWE had the highest 3-CQA and diCQAs. While, high temperature could promote the degradation of diCQAs, 3- and 4-caffeoyl are more liable to decompose as compared with 1- and 5-caffeoyl. Practical Application Over production of reactive oxygen species (ROS) in body will induce various chronic diseases. AST is an underutilized vegetable with many health benefits. This research indicates that AST possessed appreciating antioxidant activities and abundant phenolic acids, it is could be a potentail antioxidants resource and for prevention of chronic diseases associated with ROS. It also suggested that microwave could be a promising method for extracting the antioxidants in AST. Therefore, this research could lay a foundation for the high-value application of AST in food, health care and natural therapy industry, and provide some methodological references for the development of antioxidants in AST.