Background <p>Colorectal cancer is a common malignant tumor of the digestive tract with a high mortality rate. TFF3 is a secreted protein expressed in various cancers. The aim of the study is to report that inhibiting TFF3 increases the function and infiltration of CD8⁺ T cells in colorectal tumor tissues.</p> Methods <p>The proteomics analysis confirmed the high expression of secreted TFF3 in the supernatant of colorectal cancer cells, and databases were used to analyze the immune infiltration in tumor tissues. qPCR test was used to demonstrate the high levels of secreted TFF3 affecting the function of CD8⁺ T cells. In vivo experiments were used to observe the effects of TFF3 knockdown on tumor growth and immune cell infiltration. Tumor-infiltrating T lymphocytes were sorted for RNA sequencing and mechanism explanation.</p> Results <p>Inhibiting the expression of TFF3 in tumor tissues improved immune cell infiltration and enhanced anti-tumor effects. TFF3 knockdown downregulated the expression of PD-L1 in tumor tissues through the AKT/mTOR pathway, which enhanced the function of CD8⁺ T cells.</p> Conclusion <p>Knockdown of TFF3 improved the infiltration of CD8⁺ T cells and anti-tumor capabilities.</p>