ASE noise and DRBS noise are two important factors that affect the transmission performance of Raman fiber amplifiers. In this paper,the fourth-order Runge-Kutta method is used to simulate the noise power of multi-pump RFA,and the signal-to-noise ratio and noise factor of ASE and DRBS noise are further obtained. The results show that when the fiber length is smaller than 30 km,the ASE noise has a great influence on the system,while the DRBS noise is the main factor affecting the system performance when the fiber length is larger than 40 km. In addition,the noise power of the long wavelength is larger than that of the short wavelength,so has a larger effect on the system. When the wavelength difference between signals is 24 nm,the ASE noise saturation value of long wavelength is at least 0.005mw higher than that of short wavelength,and the noise saturation value of DRBS is at least 0.0025 mW higher than that of short wavelength.