A numerical method for the point defect impact in transmission fibers on back-pumped fiber Raman amplifiers (B-DFRAs) is derived, accounting to both loss and reflection effects. Characteristics of gain, amplified spontaneous Raman scattering and double Rayleigh backscattering in a B-DFRA with point defect are studied separately, and the comprehensive effect of the point defect is discussed by equivalent receiver sensitivity.