The utility model discloses an automatic water level control device in a box body of a boiler slag remover. A vertical plugging mechanism connected with a floating ball is arranged at a water inlet. When the pull rope is not straightened, the spring is in a stretched state to support the valve plate. Water level rising, floating ball lifting, tensioning pull rope, therefore, the valve plate overcomes the elastic force of the spring; slow upward movement, the water inlet amount of the water inlet is slowly reduced; therefore, the water inlet is blocked, until to stop, wHEN LIQUID LEVEL descends, reopening a water inlet, liquid is fed, and automatic liquid supplementing control is achieved; the valve plate is perpendicular to the water inlet; therefore, force application in the vertical direction is ensured; and the moving direction of the valve plate is in the vertical direction, so that the opening and closing of the valve plate are not influenced when the stress directions of the pullrope and the valve plate are vertical and the water inflow is large, water level control is prevented from being influenced when the water inflow is large, water level control is more accurate, the length of the pull rope can be adjusted, knotting is performed to shorten, the water level in the slag remover box body is adjusted, and use is more flexible.