Abstract: Multidisciplinary comprehensive treatment and whole-process multi-directional management based on systemic antitumor drugs are generally adopted in patients with advanced or metastatic gastric cancer in order to prolong survival and improve the quality of life of patients. The Chinese Society of Clinical Oncology (CSCO) guidelines for the diagnosis and treatment of gastric cancer are updated every year. The guidelines integrate the latest advances in domestic and foreign clinical research and serve to guide domestic clinical practice. The updated 2021 CSCO Guidelines for the Diagnosis and Treatment of Metastatic Gastric Cancer mainly focused on immunotherapy, anti-human epidermal growth factor receptor 2 (anti-HER2)-targeted therapy, and supportive therapy. The updated guidelines focus on the major developments in immunotherapy for advanced gastric cancer in 2020. Detailed recommendations and notes were made on the clinical application of immunotherapy (from first-line to third-line treatment), choices of different programmed death 1 (PD-1) antibodies, and different applicable populations, so as to standardize the application of immunotherapy in advanced gastric cancer. This article summarizes the updates on immunotherapy, anti-HER2-targeted therapy, and supportive care for gastric cancer in the new CSCO guidelines, in order to generalize the new progress in the treatment of advanced metastatic gastric cancer reflected in the new CSCO guidelines.