Objective To investigate the clinical factors and dosimetric parameters associated with grade≥2 radiation pneumonitis (RP) after thoracic radiotherapy in patients with locally advanced non-small cell lung cancer (NSCLC). Methods The clinical factors and dosimetric parameters in patients with locally advanced NSCLC who received thoracic radiotherapy at West China Hospital of Sichuan University between January 2016 and January 2018 were retrospectively analyzed. The potential factors associated with the occurrence of grade≥2 RP were analyzed with logistic regression analysis. Results A total of 104 patients were included, and the incidence rate of grade≥2 RP was 19.2%. Multivariate logistic regression analysis showed that the percentage of the heart volume that received more than 20 Gy (V20) [odds ratio (OR)=1.068, 95% confidence interval (CI) (1.004, 1.137), P=0.036], lung mean dose (Dmean) [OR=1.003, 95%CI (1.000, 1.006), P=0.031] and superior vena cava Dmean [OR=1.001, 95%CI (1.000, 1.001), P=0.041] were associated with grade≥2 RP. Receiver operating characteristic (ROC) curve analysis showed that the area under the ROC curve combined with heart V20, lung Dmean and superior vena cava Dmean to predict grade≥2 RP was 0.839 [95%CI (0.752, 0.926)]. In addition, the optimal critical values for heart V20, lung Dmean and superior vena cava Dmean to predict grade≥2 RP were 20%, 13 Gy and 38 Gy, respectively. Conclusions Heart V20, lung Dmean and superior vena cava Dmean are associated with grade≥2 RP after thoracic radiotherapy in patients with locally advanced NSCLC. In addition, taking heart V20<20%, lung Dmean<13 Gy and superior vena cava Dmean<38 Gy as normal organ dose limits may reduce the risk of grade≥2 RP after thoracic radiotherapy for locally advanced NSCLC patients.