ObjectiveTo evaluate the clinical, epidemiological, and viral molecular biology features of 26 patients infected with H7N9 avian influenza A virus.MethodsClinical and epidemiological data of 26 patients with confirmed avian influenza A (H7N9) infection in 2013 and 2014 were collected, virus isolated from human and poultry were identified and typed through sequencing.ResultsOf 26 patients, fever and cough were the most common symptoms, all patients had pneumonia; 20 patients（76.92%）developed acute respiratory distress syndrome(ARDS); 25 patients  (96.15%) had leucopenia or normal leukocytes at the initial diagnosis; treatment with antiviral drugs was initiated in 25 patients at a median of 10 days after the onset of illness；10 patients (38.46%)  died. Gene sequencing indicated Gln226Leu and Gly186Val substitutions in human virus H7 gene and the PB2 Asp701Asn mutation. ConclusionAcute respiratory system damage is the main clinical manifestation of avian influenza (H7N9) virus infection in humans， live poultry exposure is an important risk factor for  H7N9 infection in humans, adaptive mutation occurred at partial site of avian virus gene, which can be more easily be spread from birds to human and cause serious diseases, it is necessary to strengthen the pathogen monitoring.