An experimental device for measuring the concentration of transparent liquids is designed based on optical principles and total reflection. The liquid to be measured is contained in an acrylic plate container, which is used to study the optical path parameters when total reflection generates in the liquid. The refractive index of the transparent liquid is calculated by measuring two length parameters. Its concentration is obtained by using linear relationship between the refractive index and the concentration of transparent liquid. The measured data of sucrose solution and NaCl solution show that the relative error of refractive index is within 0.4%, and the absolute error of concentration is within 0.7%. This experimental device has the advantages of simple structure, simple operation, high measurement accuracy, low cost and obvious phenomenon.