The third plague epidemic in Harbin broke out in 1946 and ended in 1954. Different from the first two plague epidemics (imported), the third prevalence was both imported and idiopathic infectious disease which was caused by human factors. Japanese troops set forbidden zones to build a biological weapon center, which destroyed the natural environment and offered a good growth condition for Citellus Undulatus. In 1945, on the eve of surrender, the Japanese blew up the Unit 731 germ factory located in a bungalow district, which caused diffusion of infected plague fleas. Mice of the district were infected and a man - made plague focus was created. During the prevalence of the third plague, prevention departments at all levels took a series of actions and with people' s efforts, the plague was effectively controlled.