Abstract: A novel photoelectrochemical sensing platform is constructed using bismuth sulfide/porous titanium dioxide (Bi₂S₃/M-TiO₂) composite as the photoelectric active substrate for sensitive detection of Cu²⁺. The photocurrent of different photoelectric substrates materials is tested and compared using the current-time method (i-t curve). The results show that compared with single M-TiO₂, Bi₂S₃/M-TiO₂ composites exhibit significantly enhanced photocurrent response. CuS was generated by the reaction of S^2- on the surface of Cu²⁺ and Bi₂S₃/M-TiO₂, which inhibited the photocurrent intensity of the photoelectrochemical system. A high-sensitivity photochemical sensor was successfully developed for the quantitative analysis of Cu²⁺ concentration. The sensor demonstrates a strong linear response across a concentration range of 5.0×10^-10 mol/L to 1.1×10^-7 mol/L, achieving detection limits as low as 1.2×10^-8 mol/L. With its simple operation, low cost and excellent sensitivity, this sensor provides a new basis for the efficient detection of metal ions.