Inclusion Criteria:
* The subjects fully understand the purpose, nature, methods, and potential adverse reactions of the trial, voluntarily participate as participants, and sign an informed consent form (ICF) before any procedures begin
* The subject must have locally advanced or metastatic gastric cancer or gastroesophageal junction cancer that cannot be surgically removed, and the histopathological examination confirms it to be simple adenocarcinoma
* Permissible Previous Treatment: Participants with gastric cancer or gastroesophageal junction cancer who have previously received adjuvant or neoadjuvant treatment and have experienced clinical disease progression at least 6 months after the last administration are eligible for inclusion. (Note: The treatment-related toxicity of oxaliplatin in previous adjuvant or neoadjuvant treatments must be restored to the National Cancer Institute \[NCI\] General Terminology Standard for Adverse Events \[CTCAE\] v5.0 Level 1 before enrollment)
* CLDN18.2 positivity: Provide sufficient tissue markers for Claudin18.2 immunohistochemistry testing. Claudin18.2 immunohistochemistry expression ≥ 10% is confirmed as positive, and\<10% is recorded as negative
* According to RECIST v1.1 standard, there should be at least one measurable lesion
* ECOG physical state ≤ 1
* Expected lifespan\>3 months
* Adequate renal function: creatinine (Cr) ≤ 1.5 x upper limit of normal (ULN) and glomerular filtration rate (GFR) ≥ 60mL/min/1.73 m2;
* Sufficient liver function: Total bilirubin ≤ 1.5 × ULN, AST and ALT ≤ 2.5 × ULN (if there is liver metastasis, AST and ALT ≤ 5 × ULN, total bilirubin ≤ 2.5 × ULN);
* Adequate bone marrow reserve: Platelet count (PLT) ≥ 100 × 109/L, absolute neutrophil count (ANC) ≥ 1.5 × 109/L, hemoglobin ≥ 9 g/dL (no adjuvant therapy such as EPO, G-CSF, or GM-CSF has been received within 14 days, and no blood transfusion including red blood cells and platelets has been received at least 7 days before the first administration); Prothrombin time/activated partial thromboplastin time (PT/PTT)\<1.5 x ULN;
* Male or female aged ≥ 18 years old.
Exclusion Criteria:
* Known HER2 positive gastric cancer/adenocarcinoma of the gastroesophageal junction. HER2 positivity refers to HER2 amplification that requires confirmation from ISH if the HER2 immunohistochemistry test result is 3+and the immunohistochemistry test result is 2+
* Has undergone major surgery or radiation therapy within 4 weeks prior to enrollment;
* Active, known or suspected autoimmune diseases
* Congestive heart failure or symptomatic coronary artery disease within 3 months prior to enrollment
* A cerebrovascular accident occurred within the past 6 months
* Clinically significant bleeding, bleeding events, or thromboembolic diseases occur within 6 months
* History of intestinal perforation
* Have a history of (non infectious) pneumonia requiring steroid treatment or currently suffer from pneumonia
* Known history of human immunodeficiency virus (HIV) infection. Subjects with active hepatitis B or active hepatitis C. (Unless receiving antiviral therapy for at least 14 days prior to the first study drug administration and passing hepatitis B virus (HBV) DNA titer testing (not exceeding 500 IU/mL or 2500 copies \[cps\]/mL) and hepatitis C virus (HCV) RNA testing (not exceeding the lower limit of the assay), eligible for inclusion in the trial and willing to continue receiving effective antiviral therapy during the study period);
* Severe impairment of lung function or history of interstitial lung disease
* Diagnosed with concurrent malignant tumors within the past 2 years (except for fully treated non melanoma skin cancer, superficial bladder transitional cell carcinoma, and cervical carcinoma in situ \[CIS\]) or any currently active malignant tumor
* Previous or current evidence suggests that there may be confusion with the research results, interference with the participant\'s participation in the entire study process, any conditions, treatments, or laboratory abnormalities, or the researcher believes that participating in this study is not in the best interest of the participant
* Pregnancy test positive within 7 days before the first administration, or women of childbearing age who are in lactation period
* Individuals with known mental illnesses or disorders that may affect trial compliance
* Subjects who take systemic corticosteroids (\>10 mg daily prednisone equivalent) or other systemic immunosuppressive drugs (including but not limited to prednisone, dexamethasone, cyclophosphamide, azathioprine, methotrexate, thalidomide, and anti-tumor necrosis factor drugs) within 2 weeks prior to the first medication are allowed to use local, ocular, intra-articular, intranasal, and inhaled corticosteroids
* Subjects with a known history of autoimmune diseases, including but not limited to myasthenia gravis, myositis, autoimmune hepatitis, systemic lupus erythematosus, rheumatoid arthritis, Guillain Barre syndrome, multiple sclerosis, or glomerulonephritis, excluding autoimmune hypothyroidism treated with stable dose hormone replacement therapy
* Individuals with a history of previous immunodeficiency, including those with other acquired or congenital immunodeficiency diseases, or those with a history of organ transplantation, allogeneic bone marrow transplantation, or autologous hematopoietic stem cell transplantation The researcher determined that there are other situations that are not suitable for participation in this study
* The researcher determined that there are other situations that are not suitable for participation in this study
