As an advanced Raman amplification technology, third-order Raman fiber amplifiers are used in long-haul unrepeated optical transmission due to their higher gain and lower noise figure. But there is currently very limited research on it in China, and the relationship between the pump configuration and the amplifier’s performance remains unclear. Therefore, this paper analyzes the influence of second-order pump seed light on third-order Raman fiber amplifiers through experiments. First, the feasibility of not using second-order pump seed light was qualitatively analyzed. Then, it was experimentally verified that in the absence of second-order pump seed light, the third-order Raman fiber amplifier can still achieve signal light gain but at decreased efficiency. A 47-channel 200 km wavelength division multiplexing transmission system was constructed. The experimental results show that the third-order Raman fiber amplifier can amplify the signal light without the second-order pump seed light. However, introducing the second-order pump seed light can significantly improve its performance. A second-order pump seed light with only 25 mW can achieve a minimum signal power gain of 3.7 dB, an average gain of 6 dB, and an average signal-to-noise ratio gain of 0.8 dB. Eliminating second-order pump seed light can reduce costs, but introducing a second-order pump seed light brings significant performance improvements to third-order Raman amplifiers.