〔Abstract〕 Objective To investigate the expression changes of cyclin-dependent kinase inhibitor 3(CDKN3) indifferent tumors and its effect on tumor staging, prognosis and immunotherapy. Methods The expression characteristics of CDKN3 in different cancers using data from TCGA, CCLE, ICGC, and GTEx databases were evaluated. The GEPIA2 platform and Kaplan-Meier analysis were utilized to assess the effect of CDKN3 on tumor pathological staging and survival prognosis. The TIMER platform was employed to explore the influence of CDKN3 on the tumor immune microenvironment and immunotherapy. Its effect on immune checkpoint and key immunotherapeutic predictors using bioinformatics methods was explored. The GeneMANIA tool was used to construct the protein-protein interaction(PPI) network of CDKN3. Kyoto Encyclopedia of Genes and Genomes(KEGG) and Gene Onotology(GO) enrichment analyses were conducted to explore the biological processes and signaling pathways associated with CDKN3. The effect of CDKN3 on HepG2 cell proliferation, invasion, migration, and apoptosis was validated through transfection with CDKN3 siRNA. Results CDKN3 was found to be widely overexpressed in tumors. High expression of CDKN3 was often associated with advanced pathological staging and poor survival prognosis. CDKN3 expression was negatively correlated with most immune checkpoints and positively correlated with tumor mutation burden(TMB), microsatellite instability(MSI), and mismatch repair(MMR) genes. CDKN3 was associated with cell cycle, cellular senescence, and the p53 signaling pathway. Furthermore, EdU staining, JC-1 staining, Transwell, and Wound Healing assays confirmed that CDKN3 promoted HCC cell proliferation, invasion, and migration while inhibiting apoptosis. Conclusion Abnormal expression of CDKN3 is closely related to tumor staging, prognosis, and immune microenvironment characteristics, making it a potential prognostic marker and immunotherapy adjuvant target in cancer.