〔Abstract〕 Objective To investigate the mechanism of action of Jiawei Xiaoji Yinzi in the treatment of acute radiation cystitis. Methods Fifty ICR mice were randomly divided into 12 blank group and 38 modeling group. X-ray irradiator was used for modeling, and 2 mice were randomly selected and euthanized to identify whether the model was successful. The remaining mice in the modeling group were randomly divided into 12 mice in the model group, 12 mice in the xiaojiyinzi group and 12 mice in the Jiawei Xiaoji Yinzi group. The blank group, the model group, the xiaojiyinzi group, and the Jiawei Xiaoji Yinzi group were treated by gavage with 0.9 % NaCl, 0.9 % NaCl, xiaojiyinzi liquid, and Jiawei Xiaoji Yinzi liquid, respectively, once a day for 7 consecutive days. Samples were taken from mice at 24 h after the last gavage, and the enzyme-linked immunosorbent assay (ELISA) was used to measure the levels of serum superoxide dismutase (SOD), malondialdehyde (MDA), glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), Western Blot assay was used to detect mouse bladder serine/threonine kinase (AKT), E-Cadherin, endothelin-1 (ET-1), JAK kinase (JAK), nuclear transcription factor red lineage 2-related factor 2 (Nrf2), phosphatidylinositol 3-kinase ( PI3K), human chromosome 10 deletion phosphatase (PTEN), Smad protein 2 (Smad2), Smad protein 3 (Smad3), transforming growth factor β1 (TGF-β1), urinary plaque protein 3 (Upk3), and vascular endothelial growth factor (VEGF) protein relative expression levels; The relative expression levels of microRNA-21 (miR–21), PTEN, JAK, PI3K, AKT and Nrf2 messenger RNA (mRNA) in mouse bladder were detected by real-time fluorescent immuno-quantitative polymerase chain reaction (RT-PCR). Results Compared with the model group, the contents of SOD, GSH-Px, T-AOC, AKT, Mir-21, E-cadherin, JAK, Nrf2, PI3K and Upk3 in the modified Jiawei Xiaoji Yinzi group were increased (P < 0.05). The levels of MDA, ET-1, PTEN, Smad2, Smad3, Tgf-β1 and VEGF were decreased (P < 0.05). Compared with the model group and the Xiaojiyinzi group, the expression of miR-21 mRNA in the Jiawei Xiaoji Yinzi group was increased (P < 0.05). Conclusion Jiawei Xiaoji Yinzi can up-regulate the expression of miR–21 and regulate PTEN and JAK proteins to activate the downstream PI3K/AKT/Nrf2 signaling pathway in the treatment of acute radiation cystitis.