ETHNOPHARMACOLOGICAL RELEVANCE: Saffron is one of the traditional medicinal herbs, which contains various active ingredients, such as safranal, crocin, saffron acid, etc. It has anti-inflammatory, antioxidant, and anti-cancer properties, and is widely used in clinical practice. The anti-cancer efficacy of saffron has been previously confirmed, but its anti-cancer mechanism in colorectal cancer remains unclear. OBJECTIVE: We investigated the effect of active compounds of saffron on the efficacy of immunotherapy for colorectal cancer. METHODS: TCMSP and liquid chromatography-mass spectrometry analysis (LC-MS), GeneCards, and DisGeNET databases were used to identify the active compounds of saffron, drug targets and the disease targets of colorectal cancer. They were then subjected to Gene Ontology Enrichment (GO) and Signalling Pathway Enrichment (KEGG) analyses. The core targets and corresponding compounds were selected for molecular docking. The effect of active components of saffron on the proliferation of CT26 and HCT116 cells was investigated using the cell counting kit-8 (CCK-8). In vitro experiments were conducted by subcutaneous injection of CT26 cells to establish a colon cancer model. Enzyme-linked immunosorbent assay (ELISA), western blotting (WB), real-time polymerase chain reaction (RT-PCR), immunohistochemistry (IHC), and flow cytometry (FCM) were employed to validate the effects of saffron on colorectal cancer immunotherapy. RESULTS: 1. LC-MS analysis revealed that the main active component of saffron extract was crocin. The active chemicals of saffron intersected with 170 colorectal cancer targets, with 17 predicting targets for saffron treatment. GO and KEGG enrichment analyses revealed that the active components of saffron can prevent colorectal cancer development by enhancing Th17 cell differentiation and the IL-17 signaling pathway. 2. In vitro studies revealed that saffron alcohol extract, crocin, and safranal can suppress the proliferation of CT26 and HCT116 cells. 3. In vivo studies showed that crocin and safranal can increase the body mass and decrease the tumor mass of loaded mice, decrease the serum level of IL-17, and lower the mRNA expression level of IL-17, IL-6, TNF-α, TGF-β, and PD-L1 and IL-17, PD-L1 protein in tumors. This inhibitory effect was strengthened after combined immunotherapy. In addition, saffron modulated CD4+ and CD8+ T cells and the CD4+/CD8+T ratio in mouse spleens. CONCLUSION: The active components of saffron can reduce the expression of inflammatory factors and ameliorate the immunological microenvironment of tumors via the IL-17 signaling pathway, thereby improving the efficacy of immunotherapy for colorectal cancer. This study provides pharmacological support for the application of saffron in enhancing the efficacy of immunotherapy for colorectal cancer.