To investigate the effects of Buzhong Yiqi Decoction（补中益气汤）on the immune imbalance of Thelper cell 17（Th17）/regulatory T cell（Treg）and the Notch1/ROR-γt/Foxp3 signaling pathway in mice with autoimmune thyroiditis（AIT）.

Eighty CBA/J mice were randomly divided into normal group（15 mice）and model group（65 mice）. PBS＋Freund's incomplete adjuvant（IFA）was used to establish the AIT model. The mice were randomly divided into model group，Buzhong Yiqi Decoction low-dose，medium-dose and high-dose groups（4.10，8.19，16.38 g·kg^-1）and western medicine group（sodium selenite tablets，0.26 mg·kg^-1），11 mice in each group. The mice in the normal group and the model group were given the same dose of normal saline by gavage once a day，every 6 days，and stopped for 1 day，for 6 weeks. Hematoxylin-eosin（HE）staining and scanning electron microscopy（SEM）were used to observe the morphological changes of thyroid. The serum levels of thyroglobulin antibody（TgAb），thyroid stimulating hormone（TSH），free thyroid hormone（FT4），interleukin（IL）-10，IL-17A and IL-23 were detected by enzyme-linked immunosorbent assay（ELISA）. The mRNA expressions of Notch1，Foxp3 and ROR-γt in thyroid tissues were detected by Real-Time PCR. Western blot（WB）was used to detect the protein levels of Notch1，Foxp3 and ROR-γt in thyroid tissue.

Compared with those in the normal group，the serum levels of TgAb，IL-17A and IL-23 in the model group were significantly increased，while the serum level of IL-10 was significantly decreased（P<0.01）. HE staining showed that the structure of thyroid follicles in the model group was destroyed，lymphocytes were infiltrated in large sheets，and a large number of dense and slender microvilli were observed under SEM. Compared with that in the model group，the serum level of TgAb in the drug treatment groups decreased，and the changes in the Buzhong Yiqi Decoction middledose and high-dose groups and the western medicine group were more significant（P<0.01）. The serum levels of IL-17A and IL-23 of Buzhong Yiqi Decoction low-dose group were decreased，and the serum levels of IL-10 elevated（P<0.05）. The serum levels of IL-17A and IL-23 were significantly decreased，and the serum level of IL-10 was significantly increased in the Buzhong Yiqi Decoction medium-dose and high-dose groups and the western medicine group（P<0.01）. The degree of destruction of follicular epithelial cells was mild，lymphocyte infiltration was improved，and the microvilli on the cell surface was significantly reduced in each treatment group. Compared with those of the normal group，the expression levels of Notch1 and ROR-γt mRNA and protein in the thyroid tissue of the model group were significantly increased，and the expression levels of Foxp3 mRNA and protein were significantly decreased（P<0.01）. Compared with those in the model group，the expression levels of ROR-γt and Notch1 mRNA and protein in the Buzhong Yiqi Decoction groups were decreased to varying degrees，and the expression levels of Foxp3 mRNA and protein were increased to varying degrees，and those in the Buzhong Yiqi Decoction highdose group was the most significant（P<0.01）.

Buzhong Yiqi Decoction can significantly repair the pathological changes of thyroid tissue and alleviate inflammatory damage in AIT mice，mainly by regulating the Notch1/ROR-γt/Foxp3 signaling pathway to balance the immune response and establish immune function.