Progress in the mechanism research of irradiation-induced DNA single- and double-strand break are reviewed. Researches in recent years show that the yields of DNA strand breaks are related to DNA concentration and scavenging--capacity and are also influenced by DNA structure. a DSBs

induced by the one-hit event of radiation energy deposition

can be formed from both the single free radical transfer mechanism and the LMDS mechanism besides by the direct effect of radiation. For high LET radiation

αDSBs are mainly induced by the LMDS mechanism. In addition

thiol compounds have charges-related radiation protection effects on DNA. Due to the effects of the secondary free radicals of scavengers

the reverse oxygen effect can be observed for DNA strand break. Furthermore

the cylinder model of non-homogeneous kinetics is widely applied to analyze the reaction of ’OH with DNA theoretically.