• R0 resection rate [ Time Frame: up to 2 years ]
  Tumor tissue was completely resected as a percentage of all surgical patients
• pathological complete response (pCR) rate [ Time Frame: up to 2 years ]
  the rate of no residual invasive cancer, or only carcinoma in situ in both the excised breast and axillary lymph node

• Progression-free Survival (PFS) [ Time Frame: up to 2 years ]
  From date of randomization until the date of first documented progression or date of death from any cause
• Overall survival(OS) [ Time Frame: up to 2 years ]
  the first day of treatment to death or last survival confirm date

Inclusion Criteria:

1. 18-73 years old; male or female
2. confirmed gastric and gastroesophageal junction adenocarcinoma by Gastroscopic biopsy histopathological examination
3. Imaging (CT/MRI) and ultrasound gastroscopy confirmed: cT ≥ T2 and / or regional lymph node positive (N +);
4. ECOG score: 0~2 points;
5. Expected survival period ≥ 12 weeks;
6. A histological specimen can be provided for secondary testing;

7. The main organ function meets the following criteria within 7 days before treatment:

   Blood routine examination criteria (without blood transfusion within 14 days):

   Hemoglobin (HB) ≥ 90g / L; The absolute value of neutrophils (ANC) ≥ 1.5 × 109 / L; Platelet (PLT) ≥ 80 × 109 / L (2) Biochemical examinations must meet the following criteria: Total bilirubin (TBIL) ≤ 1.5 times the upper limit of normal (ULN); Alanine aminotransferase (ALT) Aspartate aminotransferase (AST) ≤ 2.5 * ULN; serum creatinine (Cr) ≤ 1.5 * ULN or creatinine clearance (CCr) ≥ 60ml / min; (3) Doppler ultrasound assessment: left ventricular ejection fraction (LVEF) ≥ normal low limit (50%).

8. Women of childbearing age should agree to use contraceptives (such as intrauterine devices, contraceptives or condoms) during the study period and within 6 months after the end of the study; negative serum or urine pregnancy test within 7 days prior to study enrollment and must be non-lactating patients; men should agree to patients who must use contraception during the study period and within 6 months after the end of the study period.
9. The patient volunteered to participate in the study and signed an informed consent form;

Exclusion Criteria:

1. Exceeding or currently suffering from other malignant tumors within 5 years, except for cervical cancer in situ, non-melanoma skin cancer and superficial bladder tumors [Ta (non-invasive tumor), Tis (in situ carcinoma) And T1 (tumor infiltrating basement membrane)];
2. Patients with a high risk of bleeding or fistula due to the apparent invasion of adjacent organs (aorta or trachea);
3. Before starting treatment， subject administrated corticosteroids (day> 10 mg equivalent dose prednisone), or other immunosuppressive drugs for systemic treatment of a disease within 14 days . In the absence of active autoimmune disease, >10 mg of daily prednisone equivalent dose of inhaled or topical steroid and adrenal replacement steroid doses are permitted;
4. Anyone who has received any anti-tumor treatment in the past;
5. Significantly malnourished patients. Exclusion is performed if the patient is receiving intravenous fluids or is required to be hospitalized for continuous infusion therapy. Patients with good nutrition control ≥ 28 days can be enrolled before randomization;
6. Participants who received live/attenuated vaccine within 30 days of the first treatment;
7. Unresolved toxicity due to any previous treatment above CTC AE4.0 Level 2, excluding neurotoxicity of ≤2 caused by hair loss and oxaliplatin;

8. Allergic reactions and adverse drug reactions:

   1. a history of allergies to the ingredients of the study drug;
   2. contraindications to any study drug (fluorouracil or oxaliplatin) in the chemotherapy regimen.

9. Patients with any severe and/or uncontrolled disease, including:

   1. patients with hypertension who are not well controlled by antihypertensive drug (systolic blood pressure ≥150 mmHg, diastolic blood pressure ≥100 mmHg);
   2. with grade I or higher myocardial ischemia or myocardial infarction, arrhythmia (including QTc ≥ 480ms) and ≥ grade 2 congestive heart failure (New York Heart Association (NYHA) classification);
   3. Severe or uncontrolled disease or active infection (≥CTCAE grade 2 infection), which the investigator believes may increase the risk associated with study participation, study drug administration, or affect the subject's ability to receive study medication;
   4. Renal failure requires hemodialysis or peritoneal dialysis;
   5. a history of immunodeficiency, including HIV-positive or other acquired, congenital immunodeficiency disease, or a history of organ transplantation;
   6. Patients with diabetes who have poor glycemic control (fasting blood glucose (FBG) > 10 mmol/L); subjects with active, known or suspected autoimmune diseases. Subjects with type 1 diabetes, residual hypothyroidism caused by autoimmune thyroiditis requiring hormone replacement therapy, and skin diseases that do not require systemic treatment (such as vitiligo, psoriasis or alopecia) can be enrolled;
   7. patients with seizures and requiring treatment;
   8. The subject has an interstitial lung disease that is symptomatic or may interfere with the discovery or management of suspected drug-related lung toxicity; previous and current subjects with a history of pulmonary fibrosis, interstitial pneumonia, pneumoconiosis, radiation pneumonitis, drug-associated pneumonia, severe impaired lung function, etc. that may interfere with the detection and management of suspected drug-related lung toxicity;
10. Patients with gastrointestinal diseases such as intestinal obstruction (including incomplete intestinal obstruction) or those who may have caused gastrointestinal bleeding, perforation or obstruction;
11. Patients who underwent surgical treatment, incisional biopsy or significant traumatic injury within 28 days prior to enrollment;
12. In the 4 weeks prior to enrollment, patients with any bleeding event ≥ CTCAE 3 have unhealed wounds, ulcers or fractures;
13. Overactive/venous thrombosis events within 3 months, such as cerebrovascular accidents (including transient ischemic attacks), deep static Pulmonary thrombosis and pulmonary embolism;
14. Prepare or accept previous allogeneic or allogeneic bone marrow transplantation, including liver transplantation;
15. According to the investigator's judgment, there is a concomitant disease that seriously harms the patient's safety or affects the patient's completion of the study;
16. Cannot perform biopsy to provide histological specimens;
17. those who have a history of psychotropic substance abuse and are unable to quit or have a mental disorder; Prepare or accept previous allogeneic or allogeneic bone marrow transplants, including liver transplants;
18. Urine routine showed urinary protein ≥ 2+ and confirmed 24-hour urine protein quantitation > 1.0 g;
19. Patients with brain metastases;
20. Patients who have participated in other clinical trials of anti-tumor drugs within four weeks.