By using the fundamental theory of the partially coherent light and the general diffraction theory, the spectral changes and spectral switch phenomenon of multicolor partial coherent light through a multi-slit system are mainly researched theoretically. The spectral changes and spectral switch phenomenon near light singularity of multicolor spatial coherent light diffracted by Fresnel zone plate are discussed. And Mathcad software is used to research spectral changes and spectral switch phenomenon of different parameters. According to theory and experimental research results, the applications of spectral changes and spectral switch in information encoding and transmission are described.