From the relation between the refractive index, viscosity, density, sound velocity and mixing ratio of mixed medium, we deduce the variation of SBS parameters, namely the Brillouin linewidth, phonon lifetime and gain coefficient, with mixing ratio. For the HT-70/FC-72 mixture, the variations of Brillouin linewidth, phonon lifetime and gain coefficient with mixing ratio are numerically simulated, and the variations of absorption coefficient and optic breakdown threshold with mixing ratio are measured in experiment. The results show that the SBS parameters exhibit a monotonic variation with mixing ratio without extrema. The use of mixed medium not only diversifies SBS medium but also optimizes the SBS system.