Abstract: Treating radiation-induced absorption as superposition of process of excitation and response, a new model is proposed to describe the radiation-induced absorption in optical fibers in space environment using the data obtained in the ground-based laboratory.There are two kinds of most important radiation in space environment: background radiation which is stable and low radiation rate and solar flare which is paroxysmal and high radiation rate.Considering the different characteristics of background radiation and solar flare, the exciting function is treated in different ways, resulting in different models.Synthesizing the different models, a new theory is obta ined out to describe the loss of optical fiber in space environment.