Tumor exosomes are nanoscale membrane-enclosed vesicles with a diameter of 30~150 nm released from tumor cells into the extracellular environment. They are present in human blood, urine, saliva and many other body fluids and are one of the biomarkers for early tumor diagnosis. Tumor exosomes have the characteristics of good stability and abundance, which is a hot spot in liquid biopsy. Tumor exosomes carry a considerable amount of molecular information derived from the originating cell such as proteins, lipids and nucleic acids, providing a variety of characteristic biomarkers that can be used for cancer detection. In this paper, the formation, isolation, characterization and detection of tumor exosomes are discussed, and the research progress of the detection of tumor exosomes is discussed in detail.