This year an outbreak of influenza in Mexico comes from a new epidemic of influenza viruses: A/H1N1 influenza virus. This virus is a kind of virus mixture, including human, avian and swine influenza virus gene fragments. The pathogenic mechanism of avian, swine and human influenza virus in its natural host were compared. The main purpose is to assess the risk of which pigs and poultry has the possibility to become one of zoonotic disease and to assess the possible role in process of avian flu transmission from pigs to people. As zoonotic disease, avian influenza and swine influenza virus have the key role in the process of human infection. But the influenza virus spread of crossing species barrier is not sufficient to cause a large outbreak of human influenza. Animal influenza viruses must have a significant genetic variation before they could live for a long term in the crowd.