<p>Gastric cancer (GC) is one of the most common and deadly types of cancer worldwide. In China, it is the most frequently occurring digestive tract tumour. Compared to traditional chemotherapeutic regimens centred on platinum and fluorouracil, immunotherapy has become one of the most important treatments for gastric cancer. Immune checkpoint inhibitors (ICIs) have the potential to benefit patients in the long term, but their development is limited by a high rate of resistance. To improve the efficacy of ICIs, it is important to understand the resistance mechanism in GC patients. In this paper, we review the resistance mechanisms of ICI in gastric cancer patients from four aspects: tumour immunity, immunosuppressed TME, tumour cells, and microbial populations.Additionally, we discuss new strategies and ideas to address ICI resistance in gastric cancer patients.</p>