All kinds of mutagenic factors may cause physiological, biochemical and genetic changes of all organisms. To characterize their characteristic biology effects, the concept of Relaxation Time (RT) was introduced for the first time, and the specific process was as follows. After mutation of organisms, the offsprings will be continuingly cultured (or cultivated) to the next generation (Rx). Once a biological effect began to show no significant difference compared to the untreated controls, the Rx was defined as the RT of the effect. In this paper, three kinds of mutagenic factors were selected to treat the seeds or seedlings of Astragalus sinicus L., subsequently, the corresponding RT was calibrated. The results showed that the RT was diverse not only among different biological effects but also among different mutagenic factors. For the RT of chemical mutagens and gamma rays, most of which are concentrated on R , whereas the heavy ion beams have significant differences among different tracks. Among biological effects, the SOD activity and superoxide anion free radical content in the Peak region are more prominent, and their RT reaches R and R , respectively. Thus, the RT may characterize the characteristic biological effects from differently mutagenic factors.