Liquid biopsy is an emerging in vitro diagnostic technology in recent years, which can detect and analyze various life information carried by screening tumor cells from the peripheral blood of patients. It is convenient, less invasive and has high detection accuracy. Circulating tumor cells (CTCs), as one of the important biomarkers of liquid biopsy, play an important role in early diagnosis, efficacy evaluation and prognosis monitoring of cancer disease. However, the level of CTCs in blood is very low, usually only 1~10 CTCs per milliliter of human whole blood, and there are tens of billions of blood cells. Therefore, the enrichment and screening of CTCs are key problems in liquid biopsy, and the analysis of the life information carried by CTCs is very significant. This paper summarizes the classical separation methods and focuses on the detection techniques of CTCs.