The invention discloses a fixed device for regulating orientation of an underwater measuring instrument for a ship, belonging to the technical field of positioning devices when underwater measurement is carried out at one side of the ship. The fixed device for regulating the orientation of the underwater measuring instrument for the ship is composed of a horizontal diverter, a fixed support, an instrument socket rack and an elevation angle regulator, wherein the horizontal diverter can realize that the measuring instrument can freely turn and position within the range of 360 degrees; and the elevation angle regulator can regulate the underwater pitch angel of the measuring instrument, wherein the regulation angle is more than or equal to 270 degrees. After all parts of the fixed device are connected, the measuring instrument is fixed on the instrument socket rack by bolts; aiming at a measuring object at a certain direction at the ship side, the horizontal angle of the fixed support is regulated in advance; meanwhile, the elevation angle regulator regulates the relative angle between the instrument socket rack and the fixed rack; then, the measuring instrument is integrally put inwater for measuring the measuring object at a certain outboard distance in a certain depth, thus precisely tracking the position variation of the measuring object, keeping the measuring object in a measuring center, and improving measuring accuracy.