The effective treatment of G/GEJ adenocarcinoma has always been a research hotspot in academia. In recent years, mainstream studies have shown that the treatment mode of G/GEJ adenocarcinoma has changed from single surgery mode in the past, to multi-disciplinary comprehensive treatment mode for now, which is based on surgery. Several studies indicate that for most late-stage G/GEJ adenocarcinoma, the neoadjuvant treatment model can further enhance the survival rates and prognosis of patients, compared with the combination of standard radical resection and postoperative adjuvant chemotherapy. According to The Chinese Society of Clinical Oncology (CSCO): clinical guidelines for the diagnosis and treatment of gastric cancer (Wang et al , 2021), neoadjuvant therapy and adjuvant therapy are recommended for patients with G/GEJ adenocarcinoma. However, there is still a lack of unified standards and norms for precise preoperative staging of gastric cancer, applicable population of neoadjuvant along with adjuvant therapy, and the selection of treatment regimens. Therefore, this project is aimed to carry out a single-arm, open-label, phase II clinical trial to administer tirelizumab plus XELOX for neoadjuvant management of patients diagnosed with resectable gastroesophageal junction or stomach cancer, and further explore the safety and therapeutic effect of chemotherapy together with tirelizumab in the neoadjuvant period of G/GEJ adenocarcinoma, eventually, providing a new option for the neoadjuvant treatment of G/GEJ adenocarcinoma.