Objective To explore the clinical feature and influencing factors of pneumonia in patients with lung cancer,in order to these patients might be timely diagnosed and treated correctly.Methods A series of 1495 cases of pneumonia in patients with lung cancer in recent 10 years were reviewed as their clinical characteristics, pathological cell types, imaging study, bacteriological monitoring, chemotherapy/radiotherapy, antibiotic treatment and prognosis.Results The infection rate of pneumonia in patients with lung cancer was 60.8%, most of them were occurred in patients treated after chemotherapy/radiotherapy, especially in patients being treated after glucocorticoid. The prognosis was poor.Conclusions The clinical situation of pneumonia in patients with lung cancer is not typical. The symptom of respiratory tract is not obvious. CT scan demonstrated obstructive pneumonia and atelectasis. Gram-negative bacteria were the mainly pathogen. The influencing factors are related to the smoking, chronic consumption, obstruction of bronchus, lower resistance after chemotherapy/radiotherapy and the basic diseases. The methods of treatment are also prelimilary discussed.