Abstract: In recent years, immunotherapy has achieved great progress in the treatment of malignant tumors and has enriched the treatment mode of many types of malignant tumors. Colorectal cancer is a common tumor worldwide. Immune checkpoint inhibitor therapy for patients with metastatic colorectal cancer (mCRC) featuring DNA mismatch repair deficiency/high microsatellite instability has significant clinical benefits, but approximately 95% of patients with mCRC are DNA mismatch repair proficient/microsatellite stable (MSS). These patients have poor response to immunotherapy. Therefore, strategies to improve the efficacy of immunotherapy in patients with this type of tumor have attracted considerable attention. This article reviews the research progress on combined immunotherapy for MSS mCRC.