A simple and rapid method has been established for the screening of the main phenolic compounds in Artemisia annua by LC-DAD-ESI-MS(n). A total of 40 phenolic compounds were identified or tentatively characterized in the methanol extract of A. annua, including 8 C-glycosyl flavonoids, 5 O-glycosyl flavonoids, 3 flavonoid aglycones, 21 quinic acid derivatives, 2 benzoicacid glucosides and 1 coumarin. The C-glycosyl flavonoids were reported from A. annua for the first time and they were found to be a new type of main constituents, and might be responsible for its antioxidant and antiviral activity. Quinic acid derivatives were also found to be the major constituents of A. annua.