The erbium-doped optical amplifier (EDFA) and erbium-ytterbium co-doped fiber amplifier optical amplifier (EYDFA) are irradiated by 60Co to simulate the condition on the low radiation dose orbits. Then the deterioration of their characters is analyzed by comparing these two kinds of fiber amplifiers. The central wavelength and half wave width of amplified signal change little in the radiation experiment, so it indicates that both of two kinds of fiber amplifiers can be applied to the inter-satellite optical communication systems. But we also find that the gain of EDFA comes down 3.91 dB, while the gain of EYDFA comes down 17.60 dB. The results indicate that ytterbium makes the antiradiation of EYDFA much worse than that of EDFA in the same radiation environment. These results also will be a good reference for space communication designers to choose the right kind of fiber amplifiers in each different system.