Highly pathogenic avian influenza A (H5N1) came to the attention of the international sci- entific community for the first time in 1997 at Hong Kong. The current global spread of hu- man infection by this subtype started in 2003. Since then, many clinical case reports on H5N1 have been reported. In 2013, China WHO reported new avian influenza virus H7N9 infected to human. After 2013 season, H7N9 infection occurred seasonally in mainly China and total number of patients reached nearly one thousand in 2016 season. Clinically, acute respiratory distress syndrome (ARDS) associated with avian influenza vi- rus infection is more severe than usual, which mortality rate reaches nearly 60%. A patholog- ical study of post-mortem biopsied lung tissues revealed that H5N1 infected alveolar epithe- lial cells and caused primary viral pneumonia, which subsequently developed into ARDS.