Objective To find new effective prevention and treatment of pregnant complications induced by placental blood supply insufficiency,the molecular mechanism of the components of Mongolian milkvetch root-Dan-shen root compound that enhanced placental blood supply was studied.Methods The effective components of Mongolian milkvetch root-Dan-shen root were extracted,nitrogen oxide synthesis blocking model was established by administration of L-Arginine methyl ester(L-NAME) to pregnant rats;and the change of the expression of iNOS mRNA in placental trophocyte was assessed by in situ hybridization to evaluate the effect of the active components of milkvetch-red sage compound. Results The expression of iNOS mRNA of model group was obviously enhanced significantly as compared with both the Mongolian milkvetch root-Dan-shen root treatment and the positive control nitroglycerin treatment groups(P<0.01).Conclusion The components of Mongolian milkvetch root-Dan-shen root compound can restrain the immune reaction of placenta,restrain the placental immune pathologic damage through the improvement of NO synthesis and release by placental trophocyte into the placental circulation,thus to keep the circulative tension between mother and fetus and to increase blood supply among uterus-placenta-fetus.