Abstract: Objective 　To identify the risk factors of radiation pneumonitis, and provide the reference standard for the clinical best treatment plan. Methods 　Pulmonary function tests ( PFTs) was measured in 78 patients with inoperable lung cancer at pre-treatment 1 week. The prognostic clinical 、dose-volume metrics and parameters PFTs of 78 patients were analysised using Chi-Square test and Logistic regression model.Prognostic clinical factors evaluated included :gender 、age、clinical stage、pathology、chemotherapy 、chronic obst ructive pulmonary disease、atelectasis、RT model 、tumor position ;dose-volume met rics :V₁₀ 、V₁₅、V₂₀ 、V₂₅ 、V₃₀ 、V₃₅ 、V₄₀、lung Dmean、effective volume (Veff ) 、gross target volume 、number of exposed fields ; parameters PFTs :forced vital capacity( Fvc) 、forced expiratory volume in 1s ( Fev 1. 0) 、diffusion capacity of carbon monoxide (DLco) . Results 　(1) 18 patient s were scored as having RT-induced pulmonary( ≥2 grade) among 78. (2) The univariate analysis revealed that many parameters (COPD、tumor volume 、V30 、DLCO ) were significantly associated with radiation2induced acute pulmonary toxicity ( P < 0. 05) .(3)Binary logistic analysis revealed that COPD and V30 > 18 % were associated with radiation-induced acute pulmonary toxicity ( P = 0. 018 and 0. 037) . Conclusion 　The radiation-induced acute pulmonary toxicity is result of many factors. To patient s with COPD or poor basic pulmonary function, V30 should be controlled below 18 % in t reatment plan.