Circulating tumor DNA (ctDNA) comes from tumor, reflecting the genetic information of the tumor well, and will change with the progress of tumor. In recent years, the unique capabilities of ctDNA have attracted much attention and been widely studied. In this paper, based on the summary of the source, properties and sample processing of ctDNA, its detection technology and application in cancer diagnosis and treatment are reviewed. The roles and importance of ctDNA reference material in second-generation sequencing are described. The urgency of establishing uniform standards and specifications of ctDNA in various processes, such as samples collection, storage, quantitative testing and data analysis, has been pointed out.