In this paper, firstly, we employed the a modified coupled-mode theory to investigate the backscattering power characteristics of Rayleigh backscattering (RB) and stimulated Brillouin scattering (SBS), synchronously and precisely. We discovered how the RB and SBS power changed with pump powers and fiber lengths. The scattering power curves with different pump powers could be divided into three regions. The first was called “the linear region of RB”, in which the pump power was mainly converted into RB and the RB power grew linearly with pump powers. The second region was called “the stimulation region of Brillouin scattering”, in which the power was mainly converted into SBS. In “the gain-saturated region”, when the pump power was much higher than the SBS threshold, both the RB and SBS power were gain-saturated. And we got the power curves with different fiber lengths. The power curves were helpful to set up proper launch powers in practical engineering applications, such as optical timedome reflectometry systems and distributed fiber sensors. Finally, we verified our theoretical results by experiments.