When a certain wavelength of light passes through the liquid，some of the light intensity will be absorbed by the liquid，and the absorption ability of different concentrations of liquid to the light intensity will be different．The remaining light intensity after liquid absorption will still cause photocurrent to be generated in the phototube．Based on the experimental principle of photoelectric effect，the corresponding photocurrent of the same liquid at different concentrations was measured．The calibration curve of the two is drawn，and the linear equation of the two is fitted by computer．That is，the corresponding concentration of the liquid can be calculated only by measuring the photocurrent of the liquid after light blocking through the photoelectric effect tester．