⁃ 1\. Sign the informed consent form; 2.18-75 years old (including 18 years old, excluding 75 years old), gender not limited; 3. The pathological histology confirmed by pathology is adenocarcinoma of the gastric/gastroesophageal junction; 4. HER2 positive tumor criteria (primary tumor or metastatic lesion, HER2 positive is defined as IHC 2+/FISH+(HER2: CEP17 ratio ≥ 2.0) or IHC (3+). Using the criteria for interpreting HER2 in gastric cancer 5. Recurrent or metastatic diseases that cannot be surgically treated, with at least one measurable lesion (RECIST 1.1 criteria) in the subject and an estimated survival time of at least 12 weeks; 6. ECOG score ranges from 0 to 1 points; 7. At least first-line systemic therapy has failed (regardless of whether it includes anti-HER2 monoclonal antibody therapy); 8. Having sufficient bone marrow, liver and kidney function:

• Absolute neutrophil count (ANC) ≥ 1.5 × 109/L, platelets ≥ 90 × 109/L, or

• hemoglobin ≥ 9g/dL;

• ALT or AST levels without liver metastasis are less than 2.5 times the upper limit of the normal range; When liver metastasis occurs, ALT or AST is less than 5 times the upper limit of the normal range; Serum bilirubin is 1.5 times lower than the upper limit of the normal reference range;

• Serum creatinine is lower than 1.5 times the upper limit of the normal reference range or creatinine clearance rate is ≥ 40ml/min; 9. Women of childbearing age and their spouses are willing to use effective contraceptive methods within the last 7 months of treatment.