A new method called as spectrophotometric titration was proposed to determine the titration endpoint of chemical oxygen demand (COD). The differences between the methods of spectrophotometri titration and national standard were analyzed. The experimental results show that the visible wavelength which can be optimally absorbed by the red-brown solution at the titration endpoint is 510 nm. The reaction rate of titration does not affect the determination of the spectrophotometric titration endpoint. The spectrophotometric titration curve can finely determine the titration endpoint. The determination errors of the titration endpoint by the two methods applied in practical samples are 1.12% and 0.84% respectively. The relative standard deviation of the spectrophotometric titration method is less than 1.20%, which is of no significant difference compared to the national standard method. The spectrophotometric titration method can determine the titration endpoint from an optical angle. It avoids the visual error by the national standard method, and provides new ideas for developing the full automation of detection instruments in the future.