Optical amplifiers have made a great achievement and a huge revolution in the world of optical communications, but some of the shortcomings must be occurs, for example, backward pump Raman amplifier suffers from decrease in gain. The main objective of this paper is to solve the problem of decrease that occurs in gain of backward pumped Raman amplifier. To solve this problem, we design a model of two of backward pumped Raman amplifiers are used in a cascaded form to overcome the attenuation in gain. We present the results in the case of using one backward pumped Raman amplifier compared to the model that we designed to show the difference between the two cases. Three types of fibers with different gain parameters are used. We also simulate and analyze the parameters that affect the Raman gain of fiber Raman amplifier for three different types of fiber. The gain depends heavily on the length of the fiber and the pumping power, according.