The stimulated Brillouin scattering(SBS) and the effect of phonon loss in SBS in optical fiber communication systems are investigated.By numerical calculations,we conclude that increasing phonon loss can improve SBS threshold.We measure the backward SBS and output light under varied input powers of fibers with different lengths.We observe the effect of the phonon blocker to the threshold of SBS,and we measure the SBS when the blocker at the different locations of the fiber.The experiments indicate that adding phonon blockcer to the transmission fiber is helpful to improve the SBS threshold,and the blocker at different locations makes different effects.In a 60 km testing fiber,the SBS threshold is the maximum when we insert the blocker at the point of 30 km.