Abstract: The reliability of converter valves based on high-power power electronic devices depends on heat dissipation via the cooling water system. Dissolved oxygen in the internal cooling water accelerates the corrosion of aluminum heat sinks and the scaling of voltage-sharing electrodes. This paper introduces dissolved oxygen content into the valve cooling system to reduce the dissolved oxygen level. The influence of the working mode and system water capacity on the deaeration efficiency, as well as the impact of flow rate on the water resistance of the deaeration device, were verified through experiments. The deoxygenation device was applied in an converter station, where a combined control strategy was adopted for deaeration, reducing the dissolved oxygen content from 6,484 ppb to 198 ppb within 13 hours. Engineering practice confirms that the proposed membrane deoxygenation technology effectively lowers the dissolved oxygen concentration, reduces nitrogen consumption, and facilitates maintenance operations of converter stations.