To explore the mechanism of Zhuyun Ⅲ, a herbal formula for spontaneous abortion by strengthening the spleen and supplementing the kidney, an abortion model with corpus luteum inhibition induced by reserpine and mifepristone (RU486) was used. One_hundred and four pregnant SD rats were allocated to seven groups:①reserpine+RU486+Zhuyun Ⅲ, ②reserpine+RU486+sijunzitang, ③reserpine+RU486+progesterone,④reserpine+RU486,⑤reserpine control,⑥RU486 control and ⑦ normal pregnant group. Different groups were observed at the same period on the level of serum progesterone(P),estradio(E 2), follicle_stimulating hormone(FSH), the positive rate of decidua progesterone receptor(PR) and the pathological changes of uterus and ovaries. The results showed that the abortion rate of group ① was lower than that of group ④ and ⑥(P<0.05). The level of serum progesterone and the positive rate of PR of group ① were all higher than that of group ②, ④ and ⑥. On the other hand, Zhuyun Ⅲ can also improve the weight reduction of body, spleen and ovary. The results indicate that Zhuyun Ⅲ exerts anti_abortion effect by promoting the secretion of corpus luteum and trophocytes, maintaining the content of target cells' receptor and relieving spleen_deficiency condition. It is also suggested that strengthening the spleen and kidney is better than supplementing the spleen only.