To meet the requirements of transmission speed and capacity for future communication systems, a Raman fiber amplifier with multiple pumped light was designed using tellurite glass fiber as transmission medium. This design takes advantage of the high non-linearity of tellurite glass fibers and enables the Raman fiber amplifier to have high gain and lower gain fluctuations than can be allowed in practical applications through cascade structure and simultaneous pumping of multiple pumped light. Based on this model, the relationship between the gain value and gain fluctuation of Raman fiber amplifier and the fiber transmission length is studied. The appropriate length of the optical fiber is determined, taking full account of the cost factors, while guaranteeing appropriate gain fluctuations and high gain values. The simulation results show that the model achieves an average gain of 39.9dB and a gain fluctuation of less than 2.1dB for signal light with 60nm bandwidth in C+L band when the first and second fiber lengths are 23m and 28m respectively. This is useful for the design of Raman fiber amplifier.