Abstract: Immunotherapy attacks tumors by activating the body’s own immune system. It is currently a research hotspot in the field of tumor treatment, and remarkable results have been achieved in a variety of malignant tumors, including gastric cancer. Solid tumors pose a challenge for immunotherapy due to their local immunosuppressive microenvironment. Diffuse-type gastric cancer, which is not sensitive to existing chemotherapy and targeted therapy, is a subtype of gastric cancer with a poor prognosis. It is therefore urgent to explore new therapies to treat this cancer subtype. Studies have shown that diffuse-type gastric cancer has a more unique immune microenvironment than intestinal-type gastric cancer. Whether or not immunotherapy can be a new treatment strategy to improve the prognosis of patients with diffuse-type gastric cancer is worth exploring. This review focuses on the tumor microenvironment of diffuse-type gastric cancer and the current status of immunotherapy and discusses the possible development direction of immunotherapy for diffuse-type gastric cancer in the future.