Based on the NOD like receptor heat protein domain associated protein 3（NLRP3）/cysteine containing aspartic protease 1（Caspase-1）/deskininoid D（GSDMD）signaling pathway，experimental autoimmune thyroiditis（EAT）model rats were used as the research subjects to explore the mechanism of action of Modified Xiaoyao Powder（逍遥散加味）in the treatment of Hashimoto's thyroiditis（HT）.

Forty SD rats were randomly assigned to a blank group（10 rats）and a model group（30 rats）. The EAT rat model was established by subcutaneous multi-point injection of pig thyroglobulin adjuvant immunoemulsion combined with drinking high iodine water. After modeling，the rats were randomly divided into a model group（10 rats），a Modified Xiaoyao Powder group（10 rats），and a selenium yeast group（10 rats）. The Modified Xiaoyao Powder group was given 7.65 g/（kg·d）Modified Xiaoyao Powder solution，the selenium yeast group was given 36μg/（kg·d）selenium yeast tablet aqueous solution，and the remaining two groups were given distilled water by gavage of equal volume. After 8 weeks，HE staining was used to observe the morphological structure of thyroid tissue in EAT rats. The ultrastructure of thyroid follicular epithelial cells in EAT rats was observed under transmission electron microscopy. Enzym-linkedimmunosorbent assay（ELISA）was used to detect the levels of serum thyroid peroxidase antibody（TPO Ab），thyroid globulin antibody（TgAb），interleukin-1β（IL-1β），and interleukin-18（IL-18）in EAT rats. Western Blot was used to detect the expressions of apoptosis related proteins in thyroid tissue cells of EAT rats.

①The results of HE staining and transmission electron microscopy showed that there was obvious pathological damage in the thyroid tissue，the membrane structure of thyroid follicular epithelial cells was blurred and damaged，the mitochondria were obviously swollen，the membrane structure was blurred and dissolved，and the rough endoplasmic reticulum was dilated. The degree of thyroid pathological damage，mitochondrial and endoplasmic reticulum damage in all treatment groups was reduced，and the degree of reduction was the most obvious in the Modified Xiaoyao Powder group.②ELISA showed that the serum levels of TgAb，TPOAb antibody，and serum levels of IL-1βand IL-18 in the model group were significantly higher than those in the blank group（P<0.01），and the serum levels of TPOAb，TgAb antibody，IL-1βand IL-18 in each treatment group were reduced（P<0.01，P<0.05），especially in the Modified Xiaoyao Powder group.③As shown by the expression level of pyroptosis-related proteins in each group by WB，the expression levels of NLRP3，GSDMD，Caspase-1 and apoptosis-associated speck-like protein containing a CARD（ASC）protein in the thyroid tissue of rats increased significantly（P<0.01），and the remaining treatment groups decreased significantly（P<0.01，P<0.05），with the decrease being the most obvious in the Modified Xiaoyao Powder group.

Modified Xiaoyao Powder alleviates the pathological damage of thyroid tissue，reduces the levels of TPOAb and TgAb antibodies，and inhibits the pyroptosis state，which may be related to the regulation of NLRP3/Caspase-1/GSDMD signaling pathway.