This is a prospective, single arm, multicenter phase II study to assess the effectiveness of Serplulimab，Trastuzumab and SOX in the adjuvant treatment of HER-2 Positive Gastric/Gastroesophageal Junction Carcinoma (GC/GEJC)
Histologically confirmed gastric adenocarcinoma/esophagogastric junction adenocarcinoma, HER-3 + or HER-2 +, with Fish amplification;
Subjects must complete R0 resection before enrollment；If they received neoadjuvant therapy, it was required that the neoadjuvant therapy regimen should not contain anti-HER-2 targeted drugs;
Postoperative pathology: II-III;
Age 18-75 years old;
A history of any other malignancy in the past 5 years (except carcinoma in situ or basal cell carcinoma of the skin or squamous cell carcinoma of the skin)；Patients with small gastric stromal tumors and other tumors may be excluded if the researcher determines that other tumors will not affect the patient's life in the short term；
Participated in clinical trials of other drugs within four weeks;
Have any active autoimmune disease or a history of autoimmune disease (e.g., but not limited to: autoimmune hepatitis, interstitial pneumonia, uveitis, enteritis, hepatitis, hypophysitis, vasculitis, nephritis, hyperthyroidism; subjects has vitiligo; asthma that has completely relieved in childhood and does not require any intervention in adulthood can be included; asthma that requires medical intervention with bronchodilators cannot be included)
Requires systemic treatment with either corticosteroids (>10 mg daily prednisone equivalents) or other immunosuppressive medications within 14 days of study drug administration to treat a current condition.