Background: This study aims to analyze the changes in thyroid structure and function in female breast cancer patients and investigate their relationship with the clinical pathological characteristics of breast cancer. Methods: The data of 169 patients treated at the Breast Surgery Department of Sichuan Province Cancer Hospital between December 2019 and January 2021 were assessed, and their preoperative serum thyroid function tests and thyroid ultrasound image data were collected. The patients were then grouped according to clinical pathological characteristics, such as tumor volume, and the differences in thyroid hormones, thyroid autoantibodies related to immunity, detection of thyroid nodules by ultrasound, and the Thyroid Imaging Reporting and Data System (TIRADS) classification of the detected nodules were compared. Additionally, we analyzed the correlation of these variables with the patients' clinical pathological characteristics. Results: Among patients with detected thyroid nodules, significant statistical differences in the TI-RADS classification of thyroid nodules found in relation to age, estrogen receptor (ER) expression, human epidermal growth factor receptor 2 (HER2) expression, histological grading and lymphovascular invasion (p < 0.05). Furthermore, a positive correlation was observed between the TI-RADS classification level of thyroid nodules and the ER expression level (G = 0.511, p < 0.001), and a negative correlation was observed with histological grading (G = -0.526, p = 0.006). However, there is no clear correlation between age groups, HER2 expression, lymphovascular invasion and the TIRADS classification level (p > 0.05), and no significant differences found in serum thyroid hormone levels and thyroid autoantibodies among breast cancer patients with different pathological characteristics (p > 0.05). Conclusions: Newly diagnosed breast cancer patients did not show notable differences in thyroid function. However, changes in thyroid structure were observed, which correlated with certain clinical pathological characteristics used to evaluate the severity of breast cancer and formulate treatment plans.