The mechanism of the radiation-induced loss in optical fibers was researched in this paper. Firstly, the structure characteristics of the pure silicon core optical fibers and traditional doped silica-core optical fibers were systematically analyzed. According to their structure characteristics, the difference of the resistance to radiation between the pure silicon core optical fibers and traditional doped silica-core optical fibers was studied. Secondly, the experimental conditions of anti-radiation standards at home and abroad were investigated. The experimental conditions including the dose rate and total dose used as anti-radiation standards had been compared. The effect of different radiation dose rates on the radiation experiments of optical fibers was analyzed. The selection principle of gamma radiation experimental conditions used in space radiation environments for fibers was given. Finally, the anti-radiation properties of a domestic pure silicon-core optical fiber with the dose rate of 0.1 rad(Si)/s were estimated, and the fiber loss after the radiation with the total dose of 20 k rad(Si) was 1.934 dB/km. The assessment results of the space radiation performances satisfied the needs of space environments for the aerospace model in the project, and the conclusion of the radiation assessment was available.