Claudin 18 isoform 2 (Claudin18.2, CLDN18.2) is a crucial structural protein involved in cell-cell tight junctions. While its expression is limited in normal tissues, it is specifically overexpressed in malignant tumors such as gastric cancer, pancreatic cancer, and esophageal cancer, making it a promising therapeutic target for cancer treatment. Recent advances in CLDN18.2-targeted therapies have been encouraging, and studies suggest that CLDN18.2-positive gastric cancer may possess a unique immune microenvironment. This raises the potential for combining targeted therapies with immune activation to achieve synergistic effects, potentially improving treatment outcomes for patients with advanced gastric cancer. This review will focus on the immune microenvironment characteristics of CLDN18.2-positive gastric cancer and summarize the current research and clinical trial progress in targeted therapies combined with immune activation for this specific cancer type.