Abstract: In order to study the characteristics of superimposed multi-wavelength fiber Bragg gratings,the coupled-mode theory of the superimposed multi-wavelength fiber Bragg gratings was presented and the numerical analysis result about the reflected spectra and time delay of 4 and 8 wavelengths superimposed FBG whose wavelength gap equals to 1.6nm was obtained.The reflected spectra of 8 wavelength superimposed FBG whose wavelength gap equal to 0.4nm is designed.The numerical result was in good agreement with the experimental results.The result show that the coupled-mode theory of the superimposed multi-wavelength fiber Bragg gratings is reliable,which can be used to analyze the characteristics of superimposed multi-wavelength fiber Bragg gratings and is conducive to the design and fabrication of superimposed multi-wavelength fiber Bragg gratings.