Space laser communication has the outstanding advantages of large transmission bandwidth, high transmission rate, and strong anti-interference ability, which is an important development direction of future communication technology. Since relay amplification cannot be realized in space laser communication links, a large transmission optical power is required in addition to ensuring a high modulation rate. Erbium-doped fiber amplifier achieves the amplification of 1.55 μm optical signal through the three-layer structure of erbium ions. The erbium-doped fiber is the core component of the erbium-doped fiber amplifier, and the erbium-doped fiber is a silicon fiber doped with a small number of erbium ions. In the space irradiation environment, high-energy particles impact the erbium-doped fiber, the core component of the erbium-doped fiber amplifier, resulting in a large number of carriers in the fiber, which combines with the original defects in the fiber to form new color-centered defects. The core defect leads to a dramatic increase in the loss of the fiber in the operating band, as well as a decrease in the gain performance of the erbium-doped fiber. As a rare earth element, La, like Er, is present in the interstitial positions of the quartz lattice structure. It can compete with Er ions for the interstitial positions and act as a dispersion of Er ions. It can achieve Al without affecting the maximum amount of Er ion doping. Low dose doping. La doping can disperse Er ions and suppress fluorescence quenching. There are few studies on the radiation effects of lanthanum-doped erbium-doped fibers. It is important to further understand the radiation-induced absorption mechanism of erbium-doped fibers to improve the performance of erbium-doped fibers in harsh environments. To verify the effect of La doping on the radiation resistance of erbium-doped fibers, two types of erbium-doped fibers, lanthanum-doped and non-lanthanum-doped, are selected in this paper, and the macroscopic radiation gain resistance performance and microstructural changes of the fibers are investigated. Radiation damage test study. The optical fiber was irradiated with a 60Co irradiation source at room temperature at a cumulative dose of 100 krad and a dose rate of 6.17 rad/s. The loss of the fiber was found to decrease along the wavelength direction in the range of 843~1 659 nm by electron probe tests and loss spectroscopy tests before and after irradiation, as well as online loss tests at specific wavelength points. However, the five fixed wavelength tests are not sufficient to fully express the loss variation of the fiber in each wavelength band under an irradiation environment. Offline loss tests were performed on both fibers before and after irradiation. The results showed that the increment before and after irradiation was 3 019 dB/km for S1 and 3 922 dB/km for S2. The loss increment of S2 after irradiation was significantly larger than that of S1 after irradiation. it was speculated that Al-OHC mainly caused the radiation-induced absorption. Absorption spectroscopy tests showed that La doping did not cause any change in the performance of Er ions in the fiber. the loss of the La-doped fiber at 1 200 nm was 0.030 67 dB/(km·krad), which was lower than 0.039 53 dB/(km·krad), and the gain of the La-doped fiber changed very little in the irradiated environment. The properties of the core matrix material did not change after irradiation by Raman testing, which proves that La doping does not cause changes in the glass lattice structure of the fiber. The paramagnetic defects of the fibers were further tested by electron paramagnetic resonance spectroscopy. The EPR signal intensities of the color-centered defects corresponding to Ge and Si did not differ much between the two types of light at 3 370 Gauss by fiber absorption spectroscopy and EPR tests. the peak at 3 330 Gauss is mainly due to the difference in Al content. the higher Al content in S2 produces a higher number of Al-OHC defects in the irradiated environment, and the corresponding EPR signal is stronger. the higher number of Al-OHC defects in S2 leads to a larger radiation-induced absorption in the 700~1 600 nm band, and the conclusion that the higher number of Al-OHC defects in S2 is consistent with the results of absorption spectroscopy tests before and after previous irradiation. The changes of Al-related paramagnetic defects in the fiber before and after irradiation were analyzed, indicating that the increase of Al content leads to more Al-OHC defects after irradiation, which in turn affects the gain performance of the fiber after irradiation. Further, by testing the gain performance of the two fibers before and after irradiation, it was found that the gain performance of the La-doped fiber changed less. It was verified that the loss and gain changes of the lanthanum- and erbium-doped fibers are smaller after irradiation, which indicates that lanthanum doping can improve the radiation resistance of the fibers. The doping of La can replace Al as the dispersant of Er ion to improve the radiation resistance of the fiber to a certain extent, and the doping of La does not negatively affect the gain performance of the fiber. This study can provide a reference for the radiation-hardening design of special optical fibers for subsequent space applications.