• The patients voluntarily joined the study and signed the informed consent; ≥ 18 years old, ≤ 75 years old, both male and female; Stage III gastric cancer confirmed by pathology, ECoG score: 0-1 Detection of biomarkers in postoperative gastric cancer samples suggests that: PD-L1 + CPS ≥ 5 / MSI-H + / EBV+/dMMR No preoperative anti-tumor treatment for gastric cancer, including chemotherapy and local treatment During the study treatment period and within 3 months after the end of the study treatment period, a medically recognized contraceptive measure (such as IUD, contraceptive pill or condom) should be used for the female patients of non-surgical sterilization or childbearing age; the serum or urine HCG test of the female patients of non-surgical sterilization must be negative within 72 hours before the study group; and the hCG test must be non lactation; for the male patients Sex, should be surgical sterilization, or agree to use appropriate methods of contraception during the trial and within 3 months after the last administration of the test drug.

⁃ The baseline blood routine and biochemical indexes of the selected patients should meet the following standards:

⁃ A. hemoglobin ≥ 90g / L

⁃ B. absolute neutrophil count ≥ 1.5 × 10 \^ 9 / L

⁃ C. platelet count ≥ 100 × 10 \^ 9 / L

⁃ D. ASTor ALT ≤ 2.5 ULN

⁃ E. Alkaline phosphatase (ALP)≤ 2.5×ULN

⁃ TSH ≤ 1 ULN (if abnormal, T3 and T4 levels should be examined at the same time, if T3 and T4 levels are normal, they can be included in the group);