The invention discloses a virus inactivating agent and an application thereof. A cinnamon extract with the final concentration of 0.5-1mg/ml is used as the virus inactivating agent. The application refers to the application of the virus inactivating agent in preparing the drug for inactivating paramyxovirus, herpes virus, retrovirus and influenza virus. The invention also discloses a virus inactivating function of the cinnamon extract (KPC-rg1). Research shows that the extract can quickly and powerfully combine with the envelope protein of virus shell under normal temperature, so that the virus is inactivated and loses infection and amplification capacity but maintains the antigenicity.