AIM: To reveal that the targeted regulation of TGF-β1 by miR-21-5P is the key mechanism that mediates the activation of myocardial fibroblasts, and to clarify the intervention ofRadix Angelica Sinensis and Radix Hedysari ultrafiltration on the mechanism of miR-21-5P targeting to regulate TGF-β1 effect.  METHODS: (1) The cells were randomly divided into normal group and irradiation group. The irradiation group received 6Gry single irradiation, and then RT-PCR was used to detect miR-21-5P, and Western Blot was used to detect the expression of α-SMA and TGF-β1. (2) The cells were randomly divided into normal group, irradiation group, miR-21-5PNC+irradiation group, miR-21-5Pinhibitor+irradiation group, and RT-PCR was used to detect miR-21-5P and Western Blot to detect the expression of TGF-β1, Smad3 and Smad7, the expression of MMP-9 and TIMP1 were detected by immunofluorescence staining, and the apoptosis was detected by EDU staining. (3) The cells were randomly divided into the normal group, the irradiation group, and the RAS-RH+ irradiation group. miR-21-5P was detected by RT-PCR, the expressions of TGF-β1, Smad3 and Smad7 were detected by Western Blot, the expressions of MMP-9 and TIMP1 were detected by immunofluorescence staining, and cell proliferation was detected by EDU staining. RESULTS: (1) The expressions of miR-21-5P, α-SMA, and TGF-β1 in the irradiation group were significantly higher than those in the normal group (P<0.05), indicating that X-ray radiation could induce the activation of myocardial fibroblasts, while miR-21-5P and TGF-β1 were closely related to the occurrence of myocardial fibrosis; (2) The expressions of miR-21-5P, TGF-β1, Smad3 and TIMP1 in the miR-21-5Pinhibitor+ irradiation group were significantly lower than those in the irradiation group, miR-21-5PNC+irradiation group, the expression of MMP-9 and Smad7 was significantly higher than that in the irradiation group, and the positive rate of EDU staining and the number of cells decreased, indicating that miR-21-5P targeted regulation of TGF-β1 was the key to mediating myocardial fibrosis (3) The expressions of miR-21-5P, α-SMA, TGF-β1, Smad3 and TIMP1 in the RAS-RH+ irradiation group were significantly lower than those in the irradiation group, and the expressions of MMP-9 and Smad7 were significantly higher than those in the irradiation group. The positive rate of staining and the number of cells decreased slightly, indicating that RAS-RH could interfere with the occurrence of radiation-induced myocardial fibrosis by inhibiting the mechanism of miR-21-5P targeting and regulating TGF-β1. CONCLUSION: RAS-RH can interfere with the occurrence of myocardial fibrosis by inhibiting the mechanism of miR-21-5P targeting and regulating TGF-β1.