Immune Checkpoint Inhibitor PD-1 Antibody Combined With Chemotherapy in the Perioperative Treatment of Locally Advanced Resectable Gastric or Gastroesophageal Junction Adenocarcinoma

Inclusion Criteria: 1. At least 18 years of age, 75 years of age or less, no gender limitation; 2. Patients with untreated locally advanced resectable adenocarcinoma of the stomach or gastroesophageal junction, with clear pathological diagnosis; 3. According to RECIST 1.1, the efficacy evaluation standard for solid tumors, there were definite measurable and evaluable lesions, with spiral CT lesions ≥1cm； 4. Physical condition score KPS score 80-100 points ； 5. Able to receive systemic chemotherapy; 6. No obvious active bleeding; 7. No history of other malignancies, except cured carcinoma in situ of the cervix, basal carcinoma of the skin or squamous cell carcinoma; 8. Women of childbearing age had negative pregnancy test and had voluntarily taken effective and reliable contraceptive measures during the clinical trial； 9. Sign the informed consent form voluntarily； Exclusion Criteria: 1. There are distant metastasis or local invasion of adjacent organs； 2. Tumor recurrence; 3. Suffered from or had previously suffered from autoimmune diseases; 4. Past organ transplantation or HIV patients; 5. Allergic to 5-fluorouracil, calcium leucoin, oxaliplatin, or irinotecan, or contraindications to 5-fluorouracil, calcium leucoin, oxaliplatin, or irinotecan exist; 6. Malignant secondary disease dating back to 5 years (exceptions: carcinoma in situ of the cervix, adequately treated basal cell carcinoma of the skin)； 7. Severe non-surgical complications or acute infections； 8. Peripheral polyneuropathy\>NCI Grad I； 9. Impaired blood system, liver and kidney function. The evaluation criteria are as follows: Blood routine: white blood cells (WBC) \<3.0×109/L, neutrophils (ANC) \<1.5×109/L, platelets (PLT) \<100×109/L, hemoglobin (Hb) \<90g/L. Liver and kidney function: total bilirubin (TBIL)\>1.5 times the upper limit of the normal value; urea nitrogen (BUN)\>1.5 times the upper limit of the normal value；Creatinine (Cr)\>1.5 times the upper limit of the normal value；Alanine aminotransferase and aspartate aminotransferase (ALT and AST)\> 3 times the upper limit of the normal value (without liver metastasis)；Alanine aminotransferase and aspartate aminotransferase (ALT and AST)\> 5 times the upper limit of the normal value (for liver metastases)； 10. Subjects with symptomatic brain metastases; 11. Subjects with obvious clinical manifestations of arrhythmia, myocardial ischemia, severe atrioventricular block, cardiac insufficiency, and severe valvular disease; 12. Subjects with severe bone marrow failure; 13. Psychotic subjects who are difficult to control； 14. Pregnant or lactating subjects; 15. Subjects whom the investigator considers inappropriate to participate in this trial； 16. Include in another clinical trial；