Abstract: Objective To investigate the clinical features of patients with connective tissue diseases(CTD) complicated with severe pneumonia. Methods Clinical data of severe pneumonia patients with CTD admitted to respiratory intensive care unit from June 2010 to May 2013 were retrospectively analyzed. Results This study included 19 patients, systemic lupus erythematosus 7 cases (36.8%), rheumatoid arthritis 5 cases (26.3%), polymyositis/dermatomyositis 3 cases(15.8%). 15 (78.9%) out of the 19 patients were treated with corticosteroids or immunosuppressants before the onset of pneumonia. The main clinical manifestations included fever (16 cases), dyspnea (17 cases), cough(12 cases). The pathogens detected in the patients included bacteria, fungi and Cytomegalovirus. Mixed infection occurred in some of the patients. After treatment, 9 patients who did not receive invasive mechanical ventilation were improved, 10 patients (noninvasive mechanical ventilation failure or receiving invasive mechanical ventilation) deteriorated or died. Conclusion Pathogens of severe pneumonia in patients with CTD include bacteria and opportunistic pathogens. Noninvasive mechanical ventilation failure and requiring invasive mechanical ventilation are poor prognostic indicators. Comprehensive diagnosis and treatment in early stage is important.