The utility model discloses a headstock gear suitable for gate fills water relates to headstock gear machinery technical field. The utility model discloses a main drive, reel device, fixed pulley, balanced pulley gear, movable pulley device and frame, balanced pulley gear is fixed in the frame, balanced pulley gear includes drive unit, leading truck and balanced loose pulley assembly, be providedwith slide rail or guide way on the leading truck, balanced loose pulley assembly cooperation is installed on the slide rail of leading truck or in the guide way, and drive unit installs on the leading truck, and links to each other with balanced loose pulley assembly, and driven equilibrium loose pulley assembly reciprocates along the guide rail or the guide way of leading truck, the utility model provides a because of height sensor trouble, electric control system trouble or people are factors such as faulty operation among the prior art, the problem that leads to the fact the excess of stroke to promote, the safe operation of guarantee hydraulic and hydroelectric engineering.