Background. The high case fatality rate of influenza A(H7N9)-infected patients has been a major clinical concern. Methods. To identify the common causes of death due to H7N9 as well as identify risk factors associated with the high inpatient mortality, we retrospectively collected clinical treatment information from 350 hospitalized human cases of H7N9 virus in mainland China during 2013-2017, of which 109 (31.1%) had died, and systematically analyzed the patients' clinical characteristics and risk factors for death. Results. The median age at time of infection was 57 years, whereas the median age at time of death was 61 years, significantly older than those who survived. In contrast to previous studies, we found nosocomial infections comprising Acinetobacter baumannii and Klebsiella most commonly associated with secondary bacterial infections, which was likely due to the high utilization of supportive therapies, including mechanical ventilation (52.6%), extracorporeal membrane oxygenation (14%), continuous renal replacement therapy (19.1%), and artificial liver therapy (9.7%). Age, time from illness onset to antiviral therapy initiation, and secondary bacterial infection were independent risk factors for death. Age >65 years, secondary bacterial infections, and initiation of neuraminidase-inhibitor therapy after 5 days from symptom onset were associated with increased risk of death. Conclusions. Death among H7N9 virus-infected patients occurred rapidly after hospital admission, especially among older patients, followed by severe hypoxemia and multisystem organ failure. Our results show that early neuraminidase-inhibitor therapy and reduction of secondary bacterial infections can help reduce mortality.