Using the spectrometer, sodium light as the light source, and the self-designed isosceles trapezoidal groove as the liquid trough, a platform for measuring the refractive index of the liquid is built. The refraction angle is easily and quickly determined by the platform, and the refractive index is obtained by programming based on Python software. The refractive index of deionized water and different concentrations of NaCl solution was measured by this method. The experimental results show that the relative error of the refractive index of the solution is far less than 5%. The method is simple in operation, fast in calculation, low in cost, high in accuracy, high in efficiency, and has strong operability and application value. It is measuring liquid refraction. It is a new method to measure the refractive index of liquid.