Objective: To study the influence of different compatibility of Astragalus Membranaceus and Salvia Miltiorrhiza on hemorheology and vascular active substances in Qi deficiency and blood stasis rat model. Methods: The SD rats were randomly divided into control group, model group, Salvia miltiorrhiza group, Astragalus membranaceus group, the compatibility of Astragalus Membranaceus and Salvia Miltiorrhiza in different proportion of 1:1, 2:1, 4:1 groups. The Qi deficiency and blood stasis rats were caused by restricted diet, forced swimming and norepinephrine subcutaneous injection. The control group and model group were given distilled water, the treatment group were given different doses of Salvia miltiorrhiza, Astragalus membranaceus and compatibility of Astragalus Membranaceus and Salvia Miltiorrhiza in different proportion of 1:1, 2:1 and 4:1 respectively by gavage for 27 days. The hemorheology and the level of endothelin-1(ET-1), nitric oxide(NO), thromboxane B2(TXB2) and 6-keto-prostaglandin F1α(6-keto-PGF1α) were determined. Compared with control group, the changes of hemorheology parameters and vascular active substances in the model group were statistically significant (P<0.01). Results: Compared with model group, the compatibility of Astragalus Membranaceus and Salvia Miltiorrhiza in proportion of 1:1, 2:1 and 4:1 groups had significantly lower hemorheology parameters(P<0.05 or P<0.01), and the content of NO, 6-keto-PGF1α, and 6-keto-PGF1α/TXB2 ratio were significantly higher (P<0.01), the level of ET-1 and TXB2 was decreased significantly (P<0.01). Compared with 1:1 groups, 2:1 groups had significantly lower hemorheology parameters (P<0.05 or P<0.01), and the content of NO, 6-keto-PGF1α, and 6-keto-PGF1α/TXB2 ratio were significantly higher (P<0.05 or P<0.01), the level of TXB2 was decreased significantly (P<0.05). Compared with 4:1 group, the changes of hemorheology parameters and vascular active substances in the 2:1 group were statistically significant (P<0.05 or P<0.01). Conclusion: The compatibility of Astragalus Membranaceus and Salvia Miltiorrhiza can improve hemorheology, protect vascular endothelium of Qi deficiency and blood stasis rats, and the compatibility of 2:1 proportion is the best. [ABSTRACT FROM AUTHOR]