Low-dose ionizing radiation becomes a focus on the domain of radiation biological effects. Theories about the harmful effects, adaptive effects and the excitatory effects of low-dose ionizing radiation are progressed. The harmful effects of low-dose ionizing radiation coexist with the non-deleterious effects, and the mechanism in which harmful effects and non-deleterious effects exist as a whole remains unclear at present. In the past, the low-dose ionizing radiation biological effects were linearly extrapolated from the high-dose effects curves. However, scientists increasingly question the validity of the linear no-threshold model in predicting the biological effects of low-dose ionizing radiation. The occurrence and mechanism of the three radiation biological effects of low-doses ionizing radiation are summarized and some may be helpful for further research project.Cited