Abstract:The mechanism of the stimulated Brillouin scattering was investigatged for the stimulated Brillouin scattering fiber optic gyros (SBS-FOG) by using non-linear theory,and the functional relation between threshold power of the fiber source and paramaters of the fiber sensing coil was educed.This relation was numerically simulated and graphically expressed for two type refractive index distribution,which provided theoretical basis for exactly choosing the parameters of the SBS-FOG.