[en] Naturalcirculation valve is a key equipment of the residual heat removal system of pool-typed low temperature heating reactor. The natural circulation valve is placed on the side wall of the reactor core vessel which can connect the fluid inside and outside the vessel together. Its natural circulation function is achieved by hydraulic closing and passive opening. When the main pump of the primary loop is running, the natural circulation valve remains closed under the normal working condition by branch jetting. After the reactor is shut down, the pressure difference between the inner and outer surfaces of the natural circulation valve is continuously reduced, and the valve is automatically opened because of its gravity. When the fluid inside and outside the vessel is connected, a nature circulation will be established because of the temperature difference and the passive removal of the residual heat of the reactor core is achieved. This is important for ensuring the safe operation of the reactor. A nature circulation valve that meets the functional requirements can be finally designed by structure design and torque balance calculation. (authors)