⁃ Voluntarily agree to participate in the research and sign the informed consent;

⁃ Age 18-70 (including 18 and 70);

⁃ Expected survival period ≥ 12 weeks;

⁃ ECOG performance status of 0 or 1 within 3 days before the first dose of study treatment;

⁃ Patients with metastatic or unresectable locally advanced or metastatic gastric cancer (including gastroesophageal junction adenocarcinoma) confirmed by histology or cytology with disease progression after standard treatment or intolerant to standard treatment;

⁃ Female subjects should be surgically sterilized, postmenopausal patients, or agree to use at least one medically approved contraceptive measure (such as an intrauterine device, contraceptives) during the study treatment period and within 6 months after the end of the study treatment period. pills or condoms), must have a negative blood pregnancy test within 7 days prior to study enrollment, and must be non-nursing. Male subjects should agree to use at least one medically approved contraceptive method during the study treatment period and within 6 months after the end of the study treatment period;

⁃ Able to understand trial requirements, willing and able to comply with trial and follow-up procedures.

‣ Adequate organ and bone marrow hematopoiesis 8. Bone marrow function:

• Hemoglobin≥90g/L;

• Absolute neutrophil count ≥1.5×109/L;

• Platelets≥100 × 109/L; 9. Liver function (subject to the normal value of the clinical trial center):

• In the absence of liver metastases, the total serum bilirubin is ≤1.5 times the ULN; in the presence of liver metastases, the total serum bilirubin is ≤3 times the ULN;

• In the absence of liver metastases, both ALT and AST are ≤3 times ULN, and in the presence of liver metastases, both ALT and AST are ≤5 times ULN; 10. Renal function (subject to the normal value of the clinical trial center):

• Serum creatinine ≤ 1.5 times ULN, or creatinine clearance (CrCl) ≥ 60 mL/min calculated by the Cockcroft-Gault formula, or 24-hour urine CrCl ≥ 60 mL/min; 11. Coagulation function: International normalized ratio (INR), activated partial thromboplastin time (APTT) and prothrombin time (PT) are all ≤1.5 times ULN; 12. Endocrine function: Thyroid-stimulating hormone (TSH) or free thyroxine (FT4) or free triiodothyronine (FT3) are within the normal range of ±10%; 13. Heart function:

• New York Heart Association (NYHA) class \<3;

• Left ventricular ejection fraction ≥50%; 14. At least one measurable lesion according to RECIST 1.1 criteria; 15. The HER2 IHC test results are IHC 1+, IHC 2+ or IHC 3+, the subject's previous test results (confirmed by the investigator) or the test results of the research center are acceptable, and can provide a diagnosis of locally advanced or metastatic gastric cancer of tumor tissue specimens, as well as a sufficient number of paraffin blocks, tissue sections (5-10 unstained) for biomarker detection.