A novel combined phase conjugator consisting of a fused silica rod and silica fiber is used in the high repetition laser system to improve the light quality. It has the advantages of higher stimulated Brillouin scattering reflectivity, higher stimulated Brillouin scattering damage threshold and lower stimulated Brillouin scattering threshold. In experiment, under the repetition rate of 100 Hz, maximum 42.05% stimulated Brillouin scattering reflectivity is obtained. According to the coupling wave equations and the boundary conditions of the experiment, the numerical value calculated from this model is in accordance with the experiment result. And the way to improve the working state of this combined phase conjugator is brought forward by our modeling.