The inclusion criteria:  Male and female aged between 18 and 75 years old. The enrolled subjects shall conform to the following criteria (Dose Escalation phase): Histologically or cytologically confirmed locally advanced or metastatic solid tumours resistant or refractory to conventional treatment, for which no conventional therapy exists or is not considered appropriate by the Investigator. (Priority for inclusion but not limited to head and neck squamous cell carcinoma, esophageal squamous cell carcinoma and breast cancer with high HER2 expression). The enrolled subjects shall conform to the following criteria (Joint extension phase): Cohort 1: Patients in recurrent/metastatic advanced head and neck squamous cell carcinoma (HNSCC) who is histologically or cytologically confirmed. The patient is also unsuitable for radical surgical resection, failed from standard treatment, or previously treated by PD-1 mAb therapy (unless patient is not suitable for PD-1 therapy). Cohort 2: Patients in advanced breast cancer (BC) with her2-overexpression who is histopathologically or cytologically confirmed, previously untreated with anti-HER2-targeted therapy such as trastuzumab or eligible for re-use though once been treated with trastuzumab. At least one targeted lesion that is measurable (according to RECIST V1.1 criteria, CT or MRI) and that lesion has not received radiation therapy. ECOG fitness score is between 0 and 1. Life expectancy of at least 3 mouths. Adequate organ function（No blood transfusion, granulocyte colony-stimulating factor (G-CSF injection, or other medical support within 14 days prior to the use of the investigational drug) The blood pregnancy test for women of reproductive age was negative during the screening period, and subjects of reproductive age (including male subjects) have no pregnancy plan and shall voluntarily use effective contraception during the trial and 6 months after the last dose. Voluntarily participate in this study and provide written informed consent.  The exclusion criteria:  Subjects with the following tumors: Malignancy other than the tumor treated in this study during the past 5 years (except for thyroid cancer, cured basal cell carcinoma of the skin, and carcinoma in situ of the cervix). Untreated central nervous system (CNS) primary tumors or metastases. Meningeal metastatic carcinoma. Patients with BMS who had previously received systemic and radical BMS treatment (radiotherapy or surgery), and who had been stable without any clinical symptoms for at least 4 weeks with systemic hormone therapy been stopped for more than 2 weeks. Subjects who have any of the following treatment history or surgical history, or who plan to receive any of the following antitumor treatments during the trial period： Patients who received proprietary Chinese medicines whose specifications explicitly included antitumor effects within 2 weeks prior to the first dose. Patients undergoing maintenance therapy within 6 months after surgery. Patients who have not recovered to normal or ≤level 1 toxicity from previous treatment (except for hair loss). Patients who received major surgery, radiation, biotherapy, or chemotherapy within 4 weeks prior to initial dose, or who were systematically treated by other investigational agents with unhealed surgical wounds, ulcers or fractures. Patients scheduled to receive any other antitumor therapy during the trial period should be excluded (except for testosterone reduction therapy in prostate cancer patients). Patients received immunosuppressants or any systemic corticosteroids within 1 week prior to the first dose. Patients previously treated with anti-HER3 drug. The subject's past medical history or laboratory examination shows any of the following abnormalities: Abnormal coagulation function with bleeding tendency or receiving thrombolytic or anticoagulant therapy or with blood loss/donation of more than 200 mL within 2 months prior to drug administration. A history of immunodeficiency, including positive HIV, or other acquired or congenital immunodeficiency disease, or a history of organ transplantation. A past history of neurological or psychiatric disorders, including epilepsy or dementia. Patients with positive TP test during screening period; with active HBV、HCV infection; except for stable hepatitis B infection by drug therapy (DNA titer not higher than 500 IU/mL or copy number <1000 copies/mL) and cured hepatitis C infection(negative HCV RNA test). Ascites, pleural effusion and pericardial effusion with clinical symptoms during the screening period, or patients requiring drainage or previously drained within 4 weeks prior to initial dose. Concommitted with a serious, progressive, or uncontrolled illness, assessed by the investigator to increase the risk of study participation during the screening period, including but not limited to: Cerebrovascular accident or transient ischemic attack (within 6 months prior to screening). Heart disease judged by the investigator to be unsuitable for the study, abnormal cardiac function or renal function with severity≥grade II. Concomitant diseases (e.g. severe hypertension, diabetes, thyroid disease, active infection, etc.) that seriously endanger patients' safety or affect patients' ability to complete the study, according to the investigator's judgment. Have a history of severe allergy, or allergic to protein products, CHO cell products, other recombinant human or humanized antibodies or components of the investigational drug. Female who is pregnant or lactating. Patients deemed unsuitable for inclusion by the investigator.