Objective: To study effect of vascular endothelia growth factor to mature mice thymocytes and to gene expression in the immune system of human. Methods: Constructed eukaryotic expression vector pCDI-VEGF plasmid and COS-7 cells were transfected. The supernatants were harvested and tested its effects on thymocytes of mice and sealed by anti-VEGF monoclonal antibodies and by signal transduction inhibitors. VEGF gene expression was detected by RT-PCR. Results: VEGF eukaryofic expression protein was found to be able to stimulate the proliferation and differentiation of murine thymocytes, monoclonal antibody against VEGF and signal transduction inhibitors can seal the effects. VEGF gene expressed in thymus and spleen of human. Conclusion: VEGF can improve the proliferation and differentiation of thymocytes of mature mouse.