A simple and sensitive electrochemical biosensor was proposed using terminal deoxynucleotidyl transferase (TdT) and dual-toehold catalytic hairpin assembly (dtCHA) for sperm DNA fragmentation analysis. The TdT extends the polyA sequences at the 3'-OH end, which triggers the dtCHA reaction and amplifies the signal, allowing for efficient measurement of the number of 3'-OH groups (equal to the quantity of breakpoints). The proposed system showed a broad linear range from 10 fM to 10 nM, with a detection limit of 7.7 fM. Furthermore, the results from clinical samples indicated that the mean quantity of DNA breakpoints (MDB) correlated more strongly with sperm motility than the commonly used DNA fragmentation index (DFI). Therefore, the platform can provide an alternative tool for sperm DNA fragmentation analysis, offering significant potential for clinical diagnosis.