Viruses are microorganisms without a cellular structure and are so tiny in diameter, measured in nanometers, that they can only be seen in an electron microscope. The shape of viruses can be classified as spherical, rod-shaped or tadpole-shaped, and the structure consists of a protein shell and the internal genetic material, which is commonly referred to as DNA and RNA. viruses can be classified into RNA and DNA viruses by their genetic material. The role of the protein shell of a virus is to protect the genetic material of the virus and inject the genetic material into the living cells of other organisms for reproduction, which is called the infection process of the virus. Viruses can only be parasitized inside living cells and once they leave the living cells they cannot survive independently and become crystalline, therefore infection of living cells is the only way for viruses to survive and reproduce. There are more than 200 known viruses, which are widely distributed, including land, sea, and sky, and can be found in all kinds of plants and animals, and almost all living things can be infected by viruses and cause diseases. Viruses cause 80% of all infectious diseases in humans, such as AIDS, influenza, smallpox, SARS, viral hepatitis, and the current pandemic of new coronaviruses. There are no specific drugs for the treatment of viruses, and the main reliance is on the patient’s immunity to resist, and the development of vaccines for viruses is a major measure to prevent viruses from causing epidemic diseases.