Abstract: Breast cancer (BRCA) is the most common malignant tumor in the world and the leading cause of death in female patients. In addition, early detection of BRCA by conventional screening methods (mammography, CT, ultrasound) is limited to a certain extent, and liquid biopsy technology has become increasingly advantageous for the early diagnosis of BRCA patients. Circulating Tumor DNA (ctDNA) is a partially free extracellular DNA present in body fluids. The ctDNA is a new idea for screening novel tumor markers based on liquid biopsy technology and helps in clinical decision-making for early breast cancer. In this paper, we discussed the biological properties of ctDNA, detection methods, and its application in the diagnosis and treatment of early BRCA, and we also look forward to the future research direction of ctDNA.