Mitochondria are semi-self-service organelles in eukaryotes. Their main function is to synthesize adenosine triphosphate (ATP), provide energy to cells through this pathway, and participate in a variety of activities within cells. These functions rely on the unique genetic material inside the mitochondria, known as mitochondrial DNA (mtDNA). Mitochondrial DNA abundance is the amount of mitochondrial DNA in a cell and is measured by the mitochondrial DNA copy number (mtDNA-CN). In recent years, as the scientific research community continues to deepen research on mitochondrial DNA abundance, and considering that blood mtDNA is relatively easier to obtain, researchers have begun to explore the potential relationship between blood mtDNA abundance and human health conditions and various diseases. Blood mtDNA abundance is increasingly considered as a possible biomarker for a variety of diseases. Research evidence has shown that blood mitochondrial DNA abundance is significantly correlated with diseases of human nervous system, kidney system and cardiovascular system, and can be used as a new biomarker for diagnosis and treatment. This review focuses on recent advances in the study of the association between blood mitochondrial DNA abundance and various human diseases.