Inclusion Criteria:
* Female and male patient ≥ 18 and ≤ 75 years.
* Histologically confirmed, medically operable, resectable adenocarcinoma of the gastroesophageal junction (AEG, Siewert II-III)，uT3, uT4a, uT4b any N category, M0, or any T N+ M0 patient
* ECOG≤1
* No previous surgical treatment, anti-tumor chemoradiotherapy/immunotherapy was performed.
* Exclusion of distant metastases by CT or MRI of abdomen, pelvis, and thorax, bone scan or MRI (if bone metastases are suspected due to clinical signs).
* Preoperative endoscopic examination confirmed no positive peritoneal implantation metastasis and exfoliated cells.
* The expected survival time is more than 6 months.
* Women of childbearing age shall be those who agree to use contraception (such as intrauterine devices, contraceptives or condoms) during the study and for 6 months after the end of the study; those who have a negative serum or urine pregnancy test within 7 days before study enrollment and must be non-lactating; and men who agree to use contraception during the study and for 6 months after the end of the study.
* Hematological, hepatic and renal function parameters adequate to allow surgical procedure and chemotherapy
* Patient able and willing to provide written informed consent and to comply with the study protocol and with the planned surgical procedures
Exclusion Criteria:
* Diagnosis of malignant diseases other than gastric cancer within 5 years prior to first administration (excluding radical basal cell carcinoma of the skin, squamous carcinoma of the skin, and/or radical resectable carcinoma in situ).
* Significant clinical bleeding symptoms or clear bleeding tendency, such as gastrointestinal bleeding, hemorrhagic gastric ulcer or vasculitis, etc. occurred within 3 months before enrollment. If fecal occult blood was positive at baseline, reexamination could be performed, if it was still positive after reexamination, gastroscopy was required.
* Prior treatment: anti-PD-1, anti-PD-L1, or anti-PD-L2 drugs or drugs that target another stimulating or co-inhibiting T-cell receptor (e.g., CTLA-4, OX-40, CD137).
* A history of immunodeficiency, including HIV testing positive.
* Is currently participating in an interventional clinical study or has been treated with another study drug or study device in the 4 weeks prior to initial dosing.
* Patients who had a history of cardiovascular and cerebrovascular diseases and were still taking thrombolytic drugs or anticoagulants orally.
* HER2 positive is known.
* Patients with previous gastrointestinal perforation, abdominal abscess or recent intestinal obstruction (within 3 months) or imaging or clinical symptoms suggesting intestinal obstruction.
