Abstract: Colorectal cancer is one of the most prevalent malignant tumors in the digestive system globally, with both its incidence and mortality showing an upward trend. In recent years, immunotherapy has become a research focus in the prognosis of CRC. Different states of tumor-infiltrating lymphocytes (TILs) in patients have distinct impacts on tumor progression. The diversity of TILs and their interactions among cells reflect the complex relationship between tumors and the immune system. Patients with mismatch repair-deficient and microsatellite instability-high (dMMR/MSI-H) molecular phenotypes exhibit higher levels of TILs. Moreover, immune checkpoint inhibitors (ICIs), which are relevant targeted drugs for immune checkpoint blockade, also demonstrate a higher response rate in colorectal cancer patients with dMMR/MSI-H molecular phenotypes. This article reviewed the basic characteristics and prognostic value of TILs, as well as the relationship between dMMR/MSI-H and the immunological characteristics of colorectal cancer patients.