Circulating tumor DNA(ctDNA), the main item of liquid biopsy, is DNA fragments from tumor genome that carries certain characteristics(including single nucleotide variation, deletion, insertion, rearrangement, copy number variation, and methylation) in the human blood circulation system. It mainly originates from apoptotic or necrotic tumor cells. The detection and analysis of ctDNA can provide genomic information in tumors, such as copy number variation, single nucleotide mutation, and methylation enrichment across the genome. It has a certain correlation with tumor size and development and considered as an emerging and promising tumor biomarker for cancer progression, reoccurrence, and routine monitoring after surgery. Compared with other tumor markers, the isolation method is relatively simple due to the stability of ctDNA. However, the extremely low abundance of ctDNA, the high content of background cell free DNA(cfDNA), the large difference between individuals, and the need of predicted detection sites in advance make it necessary to analyze ctDNA in a comprehensive way. Herein, we summarize the recent progress on ctDNA detection from digital PCR to next generation sequencing, including some commercialized apparatuses and certain methods that have recently been developed.