The author of this paper researched the source, species and distribution of the bacteria attached to the surface of Cyclops. The results indicate that the bacteria attached to the surface of Cyclops are from natural water body, and the similarity of the species between the bacteria attached to the surface of Cyclops and those in natural water body is as high as 748 ％. There is a little difference between the dominant bacteria species on the surface of Cyclops and those in natural water body. The dominant bacteria species in nature water body is not the dominant one on the surface of Cyclops. The number of free-living bacteria in natural water body is more than those attached to the surface of Cyclops. A phenomenon is found that bacteria are distributed unevenly on the surface of Cyclops by using the technology of green fluorescent protein. The bacteria mainly focus on the foot and tail of Cyclops, which are covered with specialized setae. There are also many bacteria attached to the joint of the back and abdomen of Cyclops. The oocyst of female Cyclops is another important carrier of bacteria.