A novel method measuring the Stokes elements spectral was proposed. The main idea of the method is that a modulator consisted by two retards and one polarizer is placed before the spectrometer and let the light under test go through the modulator to the spectrometer. Measuring the power spectral from the modulator only one time and executing the demodulation algorithm, the whole Stokes elements spectral from the light under test can be obtained. The disadvantages of the old methods can be removed completely by the new method. The principle for measuring the Stokes elements spectral based on the new method is deduced in detail and its feasibility is proved by the numerical simulation.