Objective To investigate the clinicopathological characteristics of HER2 protein expression in different degrees in human epidermal growth factor receptor 2 (HER2) negative breast cancer and the factors related to the efficacy of neoadjuvant chemotherapy in breast cancer with low HER2 expression. Methods The clinicopathological data of 161 patients with HER2-negative breast cancer who received neoadjuvant chemotherapy in the Department of Breast Surgery, Affiliated Hospital of Southwest Medical University from March 2019 to March 2022 were retrospectively collected. The difference of clinical and pathological characteristics of patients with different levels of HER2 protein expression were analyzed, and the factors influencing the pathological complete remission (pCR) rate of breast cancer patients with low HER2 expression after neoadjuvant chemotherapy with unconditional logistic regression model were analyzed. Results Among 161 HER2 negative breast cancer patients, 108 cases were low HER2 expression, accounting for 67.1%. Compared with those with zero expression of HER2 [immunohistochemistry (IHC) 0], the patients with low HER2 expression had higher axillary lymph node metastasis rate (P=0.048), lower histological grade (P=0.006), and higher proportion of positive hormone receptor expression (P<0.001). There was no significant difference in pCR rate among the HER2 IHC 0, IHC 1+ and IHC 2+ / in situ hybridization (ISH)– (P=0.099) , and the pCR rate of low expression of HER2 was lower than that of zero expression of HER2 in the general population and Luminal subgroup, and the difference was statistically significant (P<0.05). There was no significant difference in triple negative breast cancer subgroup (P=0.814). The logistic regression analysis showed that age, histological grade and estrogen receptor expression status were independent influencing factors for pCR rate after neoadjuvant chemotherapy with low HER2 expression (P<0.05). Conclusions Different degrees of HER2 protein expressions in patients with HER2-negative breast cancer have unique clinicopathological characteristics. The pCR rate of neoadjuvant chemotherapy in patients with low HER2-expression breast cancer is lower than that in patients with zero HER2-expression breast cancer. Age, histological grade and estrogen receptor expression status are independent factors influencing the pCR rate of neoadjuvant chemotherapy in patients with low HER2-expression breast cancer.