Abstract: Extrachromosomal circular DNA（eccDNA）, a kind of DNA molecules located the extrachromosome, widely exists in eukaryotic cells, and in which it plays a regulatory role.Studies have shown that eccDNA formed through chromosome separation or abscission, existing independently, can transcribe coding and non-coding RNAs, which is widely involved in physiological and pathological regulation of cells.Lots of works shows that the high-level expression of oncogenes comes from eccDNA transcription in the occurrence and development of tumors. In order to promote the research of eccDNA in cellular physiological and pathological function and application, this paper reviews the type, formation mechanism, physiological and pathological regulation mechanism of eccDNA.