Siwu decoction is the basic prescription for regulating blood, which can replenish blood, promote blood circulation and remove blood stasis. Siwu decoction is a well-known prescription because of its outstanding curative effect, which is divided into four parts: Angelica sinensis, Paeonia lactiflora, Rehmannia glutinosa and Chuanxiong. The whole prescription consists of blood-regulating drugs. Angelica sinensis is sweet, pungent, warm in nature, and belongs to liver, heart and spleen meridians, which has the effect of enriching blood and promoting blood circulation. But angelica and angelica tail have different functions. Angelica is good at blood, while angelica tail is good at promoting blood circulation. Paeonia lactiflora is bitter and sour, slightly cold in nature, enters the liver and spleen meridians, and has the functions of nourishing blood, astringing yin, softening liver and relieving pain. Paeonia lactiflora can be divided into Paeonia lactiflora and Paeonia lactiflora, and their effects are not exactly the same. Paeonia lactiflora is good at nourishing blood and astringing yin, and Paeonia lactiflora is good at promoting blood circulation and relieving pain. There are three kinds of rehmannia glutinosa: rehmannia glutinosa, fresh rehmannia glutinosa and dried rehmannia glutinosa. Rehmannia glutinosa is sweet, slightly warm, enters the liver and kidney meridians, and has the functions of nourishing blood, nourishing yin and replenishing marrow. Fresh Rehmannia glutinosa is good at clearing heat and cooling blood, while dried Rehmannia glutinosa is good at nourishing yin and cooling blood. Chuanxiongxin, warm in nature, enters the liver, gallbladder and pericardium meridians. It is a qi medicine in the blood, and has the functions of promoting blood circulation, promoting qi circulation, expelling wind and relieving pain. Together, these four herbs constitute the basic drugs for regulating blood, which have the peculiar effects of enriching blood without stagnation, promoting blood circulation without breaking blood, tonifying middle energizer, dispersing middle energizer and collecting middle energizer.