Si-Wu Tang (SWT), a traditional Chinese formula, is commonly used for treating female diseases, such as relief of menstrual discomfort and climacteric syndrome. The aim of this study was to explore the synergistic effects between each herb in SWT on menstrual disorder patterns. Estradiol regulation and antioxidative effects were indicators that ameliorated menstrual disorder patterns and the total polyphenol and polysaccharide contents were quality markers. According to relationships of bioactivity and phytochemical contents, we discuss the effects of each herb in SWT. In a testosterone-treated MCF-7 cell model, Rehmannia glutinosa and catalpol significantly increased the estradiol content and aromatase upregulation in cell culture. We suggest that catalpol is an aromatase promoter in SWT, and R. glutinosa is a major actor. In terms of the antioxidant activity, pentagalloylglucose, gallic acid, and ferulic acid had stronger antioxidative effects than other compounds. We suggest that the antioxidative ability depends on polyphenols, and Paeonia lactiflora is a major contributor. Based on the prescribing principle of traditional Chinese medicine (TCM) theory, we suggest that R. glutinosa in SWT act as an aromatase promoter in the role of sovereign for ameliorating menstrual disorder patterns. As P. lactiflora has the strongest antioxidant effects and can prevent ROS damage ovarian; therefore, P. lactiflora could help R. glutinosa work as a minister for menstrual disorder patterns and R. glutinosa and P. lactiflora are a herbal pair in SWT.