The invention discloses an underwater object positioning device, an underwater object positioning system and an underwater object positioning method, and relates to the technical field of underwater measurement. The underwater object positioning device comprises a control module, a buoy platform, a connecting rope, an inclinometer and a water depth sensor, wherein the inclinometer is fixedly mounted on the buoy platform, one end of the connecting rope is connected with the inclinometer, the other end of the connecting rope is connected with an underwater object, the inclinometer is used for measuring inclination angle data of the connecting rope and sending the inclination angle data to the control module, the water depth sensor is used for being mounted on the underwater object to detectdepth data of the underwater object and sending the depth data to the control module, and the control module is used for calculating three-dimensional coordinates of the underwater object relative tothe buoy platform according to the inclination angle data and the depth data. Compared with the prior art, the underwater object positioning device provided by the invention is simple in structure, low in production cost, capable of rapidly positioning the underwater object under the condition that the surrounding environment is not changed, convenient and rapid to use and high in measurement precision.