Considering the trade-off between the high gain and low noise figure in optical amplifier, a two-stage amplifier which has the structure to suppress the forward and backward-travelling amplified spontaneous emission noise with high gain and low noise figure based on Erbium-doped fiber is set up. Interpolation is used to test the power of amplified spontaneous emission (ASE) noise accurately. The gain and noise figures and some other parameters of the amplifier are analyzed. Comparison between the erbium-doped fiber amplifer (EDFA) and the commercial low noise EDFA is carried out. The results show that the highest gain of the EDFA in the experiment is 40.1 dB and the noise figure is 3.8 dB which is 0.8 dB above quantum-limit. The results when testing the amplifier and commercial EDFA in the same input power and gain show that the noise figure of the amplifier is 0.3 dB lower than the commercial EDFA.