Objective To examine the relationship between the human epidermal growth factor receptor 2 (HER2) protein expression level and clinicopathological characteristics, as well as the relationship between HER2 expression and the efficacy of neoadjuvant chemotherapy in treating HER2-positive breast cancer.Methods A retrospective analysis was conducted on the clinicopathological data from 161 patients with HER2-positive breast cancer. These patients underwent neoadjuvant chemotherapy using trastuzumab and pertuzumab from July 2019 to July 2023 in Affiliated Hospital of Beihua University. The study statistically assessed the association of the HER2 protein expression level with factors such as patients' age at diagnosis, menstrual status, tumor size, lymph node metastasis, estrogen receptor (ER), progesterone receptor (PR), Ki67, and other clinicopathologic features. Additionally, the correlation between the HER2 protein expression level, other clinicopathologic features, and the patients' pathological complete remission (pCR) post targeted combined neoadjuvant chemotherapy was also examined.Results Out of the 161 patients, 80 achieved pCR while 81 did not. The HER2 protein expression level was significantly associated with ER (χ²=21.239, P<0.001) and PR (χ²=23.733, P<0.001). Moreover, HER2 protein expression (χ²=19.940, P<0.001) and ER (χ²=26.328, P<0.001) displayed an association with pCR rates. Multifactorial analysis revealed that higher HER2 protein expression levels were observed in the ER and PR negative group (ER: O^R=0.157, 95% CI: 0.030–0.837, P=0.03; PR: O^R=0.234, 95% CI 0.065–0.841, P=0.026). Patients with a HER2 protein expression level of ICH(3+) had elevated pCR rates (O^R=6.393, 95% CI: 1.469–20.885, P=0.016), as did patients who were ER-negative (O^R=0.381, 95% CI: 0.160–0.910, P=0.030).Conclusion A significant correlation exists between the HER2 protein expression level and the hormone receptor. The HER2 protein expression level serves as a crucial predictor for the treatment outcomes of HER2-positive breast cancer patients receiving targeted drugs alongside neoadjuvant chemotherapy. Furthermore, the estrogen receptor status plays a vital role in determining the efficacy of neoadjuvant therapy.