Abstract: The transient irradiation-caused DNA damage in the human peripheral blood lymphocytes, mouse peripheral blood lymphocytes and alive mouse irradiated by α-ray and γ-ray was investigated, and the single cell gel electrophoresis(SCGE，Comet Assay) was used to detect the extent of DNA damage. On this basis, the dose-effect curve and the evaluating method for radiant after-effect were established, the absorbed dose of alive mouse A irradiated by γ-rays was computed. The results indicate that not only the dose-effect can be described by using SCGE, but also the dose-computed after organism irradiated by radiant rays is achieved with it, and SCGE may be used as a new biological dosimeter.