Abstract: Objective To study the risk factors of radiation pneumonitis in order to find prognostic parameters and provide reference standard for the best clinical treatment plan. Methods The database of PubMed, EMBASE, Cochrane Library and CNKI were searched from the date of their establishments to Februɑry 2012, and other supplied sources were also retrieved. Meta-analysis on literatures predicting radiation pneumonitis after radiotherapy were conducted by using RevMan 5.1 software. Results A total of 75 studies were included. The exposure factors included the patient's own factors （sex, age, chronic lung disease, pulmonary function, diabetes）, tumor site, therapeutic schedule （operation before radiotherapy, combined radiochemotherapy, using radiotherapy sensitization agent Amifostine）. Meta-analysis results showed that the OR and 95%CI of each factors were: 0.970.82,1.15, 0.900.63,1.28, 2.181.59,3.00, 0.270.11,0.65, 2.461.33,4.58, 0.710.57,0.90, 0.920.67,1.25, 1.411.17,1.71, 2.381.79,3.16, respectively. Conclusions The risk factors of radiation pneumonitis are chronic lung disease, pulmonary function, diabetes, tumor located in left lower lung, combined radiochemotherapy and using radiotherapy sensitization agent Amifostine. The study results indicate that upper lung cancer patients with good pulmonary function and without comorbidity such as diabetes or chronic pulmonary disease have less chance getting radiation pneumonitis based on the simple radiotherapy added with Amifostine—a radiotherapy sensitizer.