Abstract: Objective To investigate the clinical factors on postoperative radiation induced lung injury in patients with breast cancer,in order to optimize the radiotherapy plan.Method 96 patients with breast cancer who had received postoperative radiotherapy were analyzed,the relationship between the incidence of radiation injury and radiation field,radiation dose,chemotherapy drugs,age,underlying disease of the lung were observed.Results 19 patients developed radiation induced lung injury.The incidence of radiation induced lung injury were related with radiation field,radiation dose(P＜0.05).Conclusion The design of radiation field and increasing radiation dose are the major factors to increasing incidence of radiation induced lung injury in patients with breast cancer.