It is an effective approach to obtain high power laser beam output by spectral beam combining. The model of spectral beam combining using phase-shifted reflective volume Bragg gratings is established, and the diffraction characteristic is analyzed by transfer matrix method. The diffraction characteristics of reflective volume Bragg grating and phase-shifted reflective volume Bragg grating are compared. Taking the spectral beam combining of two beams by phased-shifted reflective volume Bragg gratings as an example, the effects of Gaussian monochromatic beam′s spectrum width on combining efficiency are analysed. The results show that the side-lobe of diffraction efficiency can be eliminated and the channel number can be increased by phase-shifted reflective volume Bragg gratings, and the combining efficiency can be more than 97% when the spectral beam combines of two beams with a spectral separation of 30 pm.