The aim of this study was to determine the best extraction technique, the most suitable solvent, the optimal plant parts,and the acaricidal activities of Artemisia annua L. The petroleum ether (30-60℃), petroleum ether (60-90℃), ethanol,acetone, and water parallel and sequenced extracts were obtained from the leaves, stems and roots of different period of A. annua L. in April, May, June, July and September respectively. And then the acaricidal bioactivities against Tetranychus cinnabarinus of all extracts were determined by the slide-capillary method in the laboratory. The results indicated that the acaricidal bioactivities elevated as the development of A. annua plant at the concentration of 5 mg mL-1. The general tendency exhibited the sequence of July > June > May > April, but September decreased comparing to July. However, the most effective extracts in five months were all acetone parallel extract of A. annua leaf, and the corrected mortalities treated after 48 h ranged from 74 to 100%. The median lethal concentrations (LC50) against T. cinnabarinus of acetone parallel extracts of A. annua leaves in September, July, June, May and April were 0.5986, 0.4341, 0.8376, 0.9443 and 1.3817 mg mL-1, respectively, treated after 48 h. The 13 groups were isolated from acetone extracts of A. annua leaves in July by column chromatography, both the 11th and 12th groups exhibited strong bioactivities. The median lethal concentrations of the 11th and 12th groups against T. cinnabarinus were 0.3683 and 0.1586 mg mL-1, respectively. The acetone parallel extract of A. annua leaf in July was the most toxic to T. cinnabarinus and the corrected mortality was 100% after 48 h. The acetone parallel extract of the 11th and 12th groupswere the most active components, acted as the emphases in further study.