Circulating tumor cells（ CTCs） are tumor cells that are detached from the primary tumor into the peripheral blood circulation and have a close relationship with tumor metastasis. A microfluidic chip for capturing CTCs is designed based on physical dimensions. The chip contains shunt channels

hexagonal column array for capturing cell clusters and single cell filtration channels. And combined with cellular immunofluorescence staining

using specific markers of tumor cell（ CK8 + 18、CK19、Anti-Vimentin、PD-L1） to identify CTCs. The microfluidic chip has a cell capture rate of more than 80%. CTCs are detected in 100 patients with lung cancer and in 100 healthy donors

the number of CTCs in lung cancer patients is significantly higher than that in normal people（ P < 0. 001）. The receiver operating characteristic curve（ ROC） analysis shows that the microfluidic device has apparent high sensitivity（ 92 %） and specificity（ 91 %）. In conclusion

this size-based microfluidic chip can effectively capture CTCs and characterize their biological characteristics in cancer diagnosis

which has good clinical application value.