Objective To investigate the causes of severe H1N1 Flu with multiple organ dysfunction, and measures to reduce mortality. Method The data of the patient, who was diagnosed as severe H1N1 Flu and mul-tiple organ dysfunction syndrome in First People's Hospital Affiliated to Shanghai Jiaotong University in September 2009, were retrospectively analyzed. The patient was male, 35 year-old, obese, high fever, sore throat, cough, progressive dyspnea, severe hypoxemia and hypotension. Effective measures were carried out, including protective lung ventilation, recruitment maneuver, vasopressor support, limited fluid resuscitation, appropriate corticosteroid, anfiviral plasma, anticoagulafion and antiviral medicine (Oseltamivir)in early stage and full dose. Results After one-month intensive care, clinical symptoms was improved obviously, oxygen pressure reached 74 mmHg without oxygen supply, CT scan showed diffused interstitial ehange. Neuromyopathy developed at approximately 3 weeks after the onset of H1N1. Conclusions H1N1 Flu can develop in healthy adults, and obesity is one of the inde-pendent risk factors. Effective measures should be taken as soon as possible to reduce the mortality.