The origin of smallpox virus is the evolution of poxvirus. Smallpox virus is not directly parasitic on the human body, but is a branch of the pox virus, mostly parasitic on mammals, and then through natural evolution and mutation, gradually appeared similar to cowpox infection, and mutated a variety of population susceptibility and has a great danger of viral strains, such as large smallpox, smallpox, and so on. Smallpox virus also has the contagiousness of human-to-human transmission, in the study of Egyptian mummies have found that three thousand years ago on the body of the mummy there are smallpox scars, this is the earliest traceable records, and later in the 15th century in Europe, the first century in China and other parts of the world there are smallpox outbreaks in many areas of the epidemic records, due to the death of smallpox has been more than one hundred million people in Europe. However, smallpox is now extinct in China and the general population is not at risk of contracting smallpox.