Abstract: The electrochemical sensors incorporating immunoassay principles can recognize the specific binding reaction between antigen and antibody and then convert it into an electrical signal, thus enabling rapid on-site detection of relevant disease markers in liquid samples. In this work, an electrochemical sensor for the detection of the bladder cancer marker cytokeratin 18 (CK18) was constructed based on the chemically modified electrode. The electrode surface was modified by semiconductor colloidal quantum dots (CQDs), and the significant surface effect, size effect and unique quantum effect of CQDs were utilized to improve the enrichment and signal transduction of biomolecules on the work electrode. The results showed that the interface of carbon electrode with lead sulfide (PbS) CQDs was stable with good charge transfer capability. The electrode surface was then coated with anti-cytokeratin 18 antibody and sealing agent to finish the electrode preparation. When measured with differential pulse voltammetry (DPV) mode, which could significantly reduce the background current for electrochemical performance testing, the sensor exhibited the sensing performance of CK18 antigen with the detection time of about 30 s, and the detection limit of 58 fg mL^-1, which possessed the characteristics of high sensitivity, easyto-use, and non-invasive detection, indicating the potential of the application in the early screening of bladder cancer and other diseases.