Abstract: Radiation pneumonitis (RP) is one of the most common toxicities in patients with lung cancer treated by radiotherapy, which limits the delivered dose and may thus hampers tumor control, then lowers the patients^, life quality. Based on the progress of molecular biology, RP may be regarded as a continuous progression of events induced by various cytokines involving numerous cells. Researches on gene polymorphisms indicate different mechanisms in the pathogenesis of RP among different races. Besides, more studies focus on the predictive value of dosimetric parameters such as V₂₀、mean lung dose(MLD) and biological markers such as transforming growth factor-β(TGF-β1).Decreasing use of drugs which may exacerbate RP and increasing use of modern treatments may be beneficial in the prevention. Meanwhile as the respect of drug prevention, more and more emphases are being placed on the target molecule of radiation-induced injury.