Abstract: Exsomes are a kind of endocytosis-derived small vesicles with a size of 50- 100 nm，containing microRNA, mRNA, DNA fragment, protein and so on. They were secreted by immune cells, mesenchymal cells, tumor cells and many other kinds of cells through exocytic pathway, mainly transferred from donor cells to recipient cells. Tumor-derived exosomes have close relationship with tumor progression. On one hand, tumor-derived exosomes contributed to the construction of tumor microenvironment, on the other hand, tumor-derived exosomes have dual function of immunoenhancement and immunosuppression in human immune system. Exosomes have a potential to be biomarker in diagnosis and treatment of tumor. In this article, we will discuss the biogenesis and secretion of exosomes, and mainly emphasizes the function of tumor-derived exosomes in tumor microenvironment and immune system, and its prospect of clinical application.