The invention relates to a single-joint water machine fish which comprises a shell, a main board cabin, a motion control cabin and a battery cabin; the outer contour of the shell is in a bionic fish shape, one end of the connecting rod is a front shell, and the other end of the front shell is of a bionic fishtail structure, and the front end of the main board cabin is matched and installed with the inner side of the front casing, wherein a lens set is arranged in the main board cabin, an eccentric anti-shake mechanism and a main PCB (printed circuit board), wherein the motion control cabin is connected with the rear end of the main board cabin, a three-axis linkage device and a transmission device are arranged in the motion control cabin, and the battery cabin is arranged below the motion control cabin according to the single-joint water machine fish disclosed by the invention, the special design is adopted for the single-joint water machine fish, the functions of water depth detection, water quality monitoring, underwater photography, underwater exploration, fish school detection, feeding, drug delivery, underwater engineering acceptance and underwater communication, underwater salvage, underwater rescue, seaborne rescue, sea, river, lake bed surveying and mapping, underwater drilling and flaw detection and the like can be realized.