In recent years, major projects in the field of space science such as the starlink proposed by Space X, Micius satellite for quantum science experiments, gravitational wave detection, and space-earth integration network put forward urgent demands for lasers for space applications. Fiber lasers have the advantages of high brightness, good robustness, and high power-to-weight ratio, and have important applications in space laser communication, radar, remote sensing, space debris treatment, etc. [1–3]. Rare earth ions (Yb3+, Er3+, Er3+-Yb3+, Tm3+, etc.) doped silica fiber, also known as “active fiber”, is the core gain medium that constitutes the fiber laser. Its function is to generate lasers and achieve gain amplification. Space is a complex environment that includes strong radiation, high vacuum, and large temperature differences. When the fiber laser is subjected to space ionizing radiation, the optical loss and noise factor of the active fiber will increase sharply, and the laser slope efficiency or gain performance will drop significantly. This phenomenon is called the radiation-induced darkening (RD) effect [4, 5], the fundamental reason is related to the color centers produced by irradiation. In addition, the absorption loss of color centers will also increase the thermal effect of active fibers, leading to a significant decrease in the threshold of transverse mode instability (TMI), severely restricting the output performance of fiber lasers. How to effectively solve the RD effect of active fibers for space applications is a difficult problem faced by researchers at home and abroad. It is necessary to conduct systematic research from the perspectives of the RD generation mechanism, influencing factors, and suppression methods.