• Voluntarily agree to participate in the study and sign the informed consent;

• Subjects aged 18-70 years (including 18 years and 70 years) and not reaching the 71st birthday were all considered to be ≤70 years old;

• Expected survival ≥12 weeks;

• Eastern Cooperative Oncology Group(ECOG) physical condition 0 or 1;

• For female subjects of child-bearing age women agreed to study during treatment and experimental subjects within 6 months after the end of the treatment period using an approved by the medical contraception (e.g. intrauterine device, the pill or condoms), before the study drug delivery within 7 days of pregnancy blood test must be negative (sterilization surgery or age 60 or more subjects can choose no pregnancy blood test), and must be an lactation. For male subjects: should be sterilized surgically, or agree to use a medically approved contraceptive method during the study period and for 6 months after the end of the treatment period. Control subjects after the end of the treatment period according to the choice of control drugs to determine the length of contraception.

• Able to understand the study requirements and be willing and able to follow the study and follow-up procedures.

• Bone marrow function:

⁃ hemoglobin ≥9g/dL; absolute neutrophil count ≥1.5×109/L; white blood cell count ≥3.0×109/L platelet ≥100 ×109/L;

• Liver function (according to the normal value of the clinical trial center) :

⁃ serum total bilirubin ≤1.5 times the upper limit of normal value (ULN); alanine aminotransferase (ALT), aspartate aminotransferase(AST) and Alkaline phosphatase（ALP） were ≤2.5 × ULN in the absence of liver metastasis, and ALT, AST and Alkaline phosphatase(ALP) were ≤5 × ULN in the presence of liver metastasis

• Renal function (according to the normal value of the clinical trial center) :

⁃ serum creatinine ≤1.5×ULN, or calculated by Cockcroft-Gault formula, the creatinine clearance rate (CrCl) ≥60 mL/min;

• Cardiac function:

⁃ American New York college of cardiology (NYHA) grade \< 3; left ventricular ejection fraction ≥50%;

• Breast cancer subjects diagnosed by histology and / or cytology are currently at a locally advanced or metastatic stage and cannot be radically removed;

• The low expression of HER2 confirmed by the IHC and FISH results of the central laboratory (defined as: IHC 2+ and no amplification of FISH); the subject can provide a specimen of the primary or metastatic tumor site (paraffin wax) for HER2 detection Block, paraffin-embedded section or fresh tissue section can be used);

• Previous use of anthracycline drugs;

• Received 1 or 2 systemic chemotherapy treatments after relapse / metastasis. Subjects who relapsed during adjuvant chemotherapy or within 12 months after the end of adjuvant chemotherapy were considered to have failed first-line chemotherapy after relapse / metastasis.

• Hormone receptors are negative or positive. Hormone receptor-positive subjects need to progress after receiving endocrine therapy after relapse / metastasis or relapse after less than 2 years. Patients who are not suitable for endocrine therapy can be included in this study after undergoing chemotherapy treatment (first-line or second-line);

• The imaging evidence confirmed by the investigator that the tumor disease progressed during or after the most recent treatment is required;

• There has been no diagnosis of HER2 positive (HER2 IHC 3+ or FISH amplification)

• Have not used drugs targeting HER2 (including antibodies, small molecule Tyrosine kinase inhibitor（TKIs） and antibody drug conjugates).

• According to the RECIST 1.1 standard, there is at least one measurable lesion.