Objective To investigate the related factors of radiation-induced lung injury (RILI) in three-dimensional conformal intensity modulated radiation therapy (IMRT) for middle and lower esophageal cancer, and to provide evidence for the selection of radiotherapy for esophageal carcinoma. Methods 72 cases of esophageal cancer patients in our hospital from May 2011 to May 2014 were selected for the radiotherapy. The varian Ix-6074 linear accelerator and Eclipse 11 radiotherapy planning system was applied to produce plan, and the whole prescription dose (60~68) Gy/ (30~34) F, 95% of the planning target volume (PTV) reached the prescribed dose under the premise of using dose volume histogram (DVH) of lung tissue by comparison when the irradiation dose volume and RILI, and to explore the correlation between clinical factors and RILI. Results Follow up study revealed the one-year overall survival rate of 94.44%. In the middle and lower esophageal cancer patients, the length of tumor lesion, the COPD and the total dose of radiotherapy were associated to the incidence of RILI after IMRT. 9 cases of the 72 patients had found radiation-induced lung injury (12.50%). There was significant difference between the patients of RILI and the patients of no radioactive lung injury for the V10, V15, V20, V30 and Dmean (all P<0.05), however, V5, V25, V35, V40, Dmax and Dmin in the patients between the two groups showed no significant difference (all P>0.05). Conclusions V10, V15, V20, V30 and lung Dmean dose of lung are the key factors of RILI. Radiation dosimetry in IMRT for esophageal carcinoma can predict the incidence of radiation-induced lung injury better.