Circulating free DNA (cfDNA) refers to the free DNA nucleotides in body fluids, but the dynamic response in vivo tumor load and full assessment of genetic heterogeneity in cancer patients provides a non-invasive diagnostic approach. It is one of the effective biomarkers for cancer screening and diagnosis, and also provides for the prognosis for patients with advanced cancer and forecast information. In this paper, the clinical application of cfDNA is reviewed.