Due to the uneven output gain and low gain of single pump Raman fiber amplifier(RFA), the performance of optical fiber communication system becomes worse. A forward three pumps RFA is designed. Focusing on the influence of the appropriate number of pumps, pump wavelength and pump power on the output gain of RFA, and combining with OptiSystem software, the gain of L-band RFA is optimized and simulated. The simulation results show that the designed RFA achieves a gain of more than 10 dB in L-band and is relatively flat. The maximum gain is 18.9 dB and the maximum noise figure is 8.0 dB.